[FIRRTL] Crash with fstring type on port

fstring type would never be on port from the current fir parser but it crashes at LowerToHW:

```mlir
firrtl.circuit "Printf"{
// CHECK-LABEL: module Printf
firrtl.module @Printf(in %clock: !firrtl.fstring) attributes {convention = #firrtl} {
}
}
```

```
$ firtool bar.mlir

firtool: /scratch/hidetou/circt/lib/Conversion/FIRRTLToHW/LowerToHW.cpp:2562: llvm::LogicalResult (anonymous namespace)::FIRRTLLowering::setLowering(mlir::Value, mlir::Value): Assertion `(!result || !type_isa(result.getType())) && "Lowering didn't turn a FIRRTL value into a non-FIRRTL value"' failed.
PLEASE submit a bug report to https://github.com/llvm/circt and include the crash backtrace.
Stack dump:
0. Program arguments: ./build/bin/firtool bar.mlir
#0 0x00000000007ceb97 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /scratch/hidetou/circt/llvm/llvm/lib/Support/Unix/Signals.inc:804:13
#1 0x00000000007ccad0 llvm::sys::RunSignalHandlers() /scratch/hidetou/circt/llvm/llvm/lib/Support/Signals.cpp:106:18
#2 0x00000000007cf4aa SignalHandler(int, siginfo_t*, void*) /scratch/hidetou/circt/llvm/llvm/lib/Support/Unix/Signals.inc:0:3
#3 0x00007f083c2b1cf0 __restore_rt (/lib64/libpthread.so.0+0x12cf0)
#4 0x00007f083b36aacf raise (/lib64/libc.so.6+0x4eacf)
#5 0x00007f083b33dea5 abort (/lib64/libc.so.6+0x21ea5)
#6 0x00007f083b33dd79 _nl_load_domain.cold.0 (/lib64/libc.so.6+0x21d79)
#7 0x00007f083b363426 (/lib64/libc.so.6+0x47426)
#8 0x0000000000d2176a decltype(auto) llvm::dyn_cast(mlir::Type const&) /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/Casting.h:650:3
#9 0x0000000000d2176a decltype(auto) llvm::detail::TypeSwitchBase, mlir::Type>::castValue(mlir::Type const&) /scratch/hidetou/circt/llvm/llvm/include/llvm/ADT/TypeSwitch.h:67:12
#10 0x0000000000d2176a llvm::TypeSwitch& llvm::TypeSwitch::Case(circt::firrtl::getBaseType(mlir::Type)::'lambda0'(auto)&&) /scratch/hidetou/circt/llvm/llvm/include/llvm/ADT/TypeSwitch.h:101:26
#11 0x0000000000d2176a circt::firrtl::getBaseType(mlir::Type) /scratch/hidetou/circt/include/circt/Dialect/FIRRTL/FIRRTLUtils.h:225:8
#12 0x0000000000d2176a (anonymous namespace)::FIRRTLLowering::setLowering(mlir::Value, mlir::Value) /scratch/hidetou/circt/lib/Conversion/FIRRTLToHW/LowerToHW.cpp:2565:21
#13 0x0000000000d1ee1f llvm::LogicalResult::failed() const /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:43:43
#14 0x0000000000d1ee1f llvm::failed(llvm::LogicalResult) /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:71:58
#15 0x0000000000d1ee1f (anonymous namespace)::FIRRTLLowering::run() /scratch/hidetou/circt/lib/Conversion/FIRRTLToHW/LowerToHW.cpp:1985:9
#16 0x0000000000d1ee1f (anonymous namespace)::FIRRTLModuleLowering::lowerModuleOperations(circt::hw::HWModuleOp, (anonymous namespace)::CircuitLoweringState&) /scratch/hidetou/circt/lib/Conversion/FIRRTLToHW/LowerToHW.cpp:1977:48
#17 0x0000000000d152a8 llvm::LogicalResult::failed() const /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:43:43
#18 0x0000000000d152a8 llvm::failed(llvm::LogicalResult) /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:71:58
#19 0x0000000000d152a8 llvm::LogicalResult mlir::failableParallelForEach, (anonymous namespace)::FIRRTLModuleLowering::runOnOperation()::$_10>(mlir::MLIRContext*, llvm::detail::SafeIntIterator, llvm::detail::SafeIntIterator, (anonymous namespace)::FIRRTLModuleLowering::runOnOperation()::$_10&&) /scratch/hidetou/circt/llvm/llvm/../mlir/include/mlir/IR/Threading.h:46:11
#20 0x0000000000d152a8 llvm::LogicalResult mlir::failableParallelForEach, (anonymous namespace)::FIRRTLModuleLowering::runOnOperation()::$_10>(mlir::MLIRContext*, llvm::iota_range&&, (anonymous namespace)::FIRRTLModuleLowering::runOnOperation()::$_10&&) /scratch/hidetou/circt/llvm/llvm/../mlir/include/mlir/IR/Threading.h:92:10
#21 0x0000000000d152a8 llvm::LogicalResult mlir::failableParallelForEachN<(anonymous namespace)::FIRRTLModuleLowering::runOnOperation()::$_10>(mlir::MLIRContext*, unsigned long, unsigned long, (anonymous namespace)::FIRRTLModuleLowering::runOnOperation()::$_10&&) /scratch/hidetou/circt/llvm/llvm/../mlir/include/mlir/IR/Threading.h:107:10
#22 0x0000000000d152a8 (anonymous namespace)::FIRRTLModuleLowering::runOnOperation() /scratch/hidetou/circt/lib/Conversion/FIRRTLToHW/LowerToHW.cpp:753:17
#23 0x000000000148cff9 mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int)::$_7::operator()() const /scratch/hidetou/circt/llvm/mlir/lib/Pass/Pass.cpp:0:17
#24 0x000000000148cff9 void llvm::function_ref::callback_fn(long) /scratch/hidetou/circt/llvm/llvm/include/llvm/ADT/STLFunctionalExtras.h:46:12
#25 0x000000000148cff9 llvm::function_ref::operator()() const /scratch/hidetou/circt/llvm/llvm/include/llvm/ADT/STLFunctionalExtras.h:69:12
#26 0x000000000148cff9 void mlir::MLIRContext::executeAction(llvm::function_ref, llvm::ArrayRef, mlir::Pass&) /scratch/hidetou/circt/llvm/mlir/include/mlir/IR/MLIRContext.h:288:7
#27 0x000000000148cff9 mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) /scratch/hidetou/circt/llvm/mlir/lib/Pass/Pass.cpp:520:21
#28 0x000000000148fdbf llvm::LogicalResult::failed() const /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:43:43
#29 0x000000000148fdbf llvm::failed(llvm::LogicalResult) /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:71:58
#30 0x000000000148fdbf mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) /scratch/hidetou/circt/llvm/mlir/lib/Pass/Pass.cpp:592:9
#31 0x000000000148fdbf mlir::PassManager::runPasses(mlir::Operation*, mlir::AnalysisManager) /scratch/hidetou/circt/llvm/mlir/lib/Pass/Pass.cpp:905:10
#32 0x000000000148fdbf mlir::PassManager::run(mlir::Operation*) /scratch/hidetou/circt/llvm/mlir/lib/Pass/Pass.cpp:885:60
#33 0x0000000000758686 llvm::LogicalResult::failed() const /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:43:43
#34 0x0000000000758686 llvm::failed(llvm::LogicalResult) /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:71:58
#35 0x0000000000758686 processBuffer(mlir::MLIRContext&, circt::firtool::FirtoolOptions&, mlir::TimingScope&, llvm::SourceMgr&, std::optional>>&) /scratch/hidetou/circt/tools/firtool/firtool.cpp:561:7
#36 0x00000000007572fb processInputSplit(mlir::MLIRContext&, circt::firtool::FirtoolOptions&, mlir::TimingScope&, std::unique_ptr>, std::optional>>&) /scratch/hidetou/circt/tools/firtool/firtool.cpp:619:12
#37 0x0000000000752e60 processInput(mlir::MLIRContext&, circt::firtool::FirtoolOptions&, mlir::TimingScope&, std::unique_ptr>, std::optional>>&) /scratch/hidetou/circt/tools/firtool/firtool.cpp:635:12
#38 0x0000000000752e60 executeFirtool(mlir::MLIRContext&, circt::firtool::FirtoolOptions&) /scratch/hidetou/circt/tools/firtool/firtool.cpp:727:14
#39 0x0000000000751288 llvm::LogicalResult::failed() const /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:43:43
#40 0x0000000000751288 llvm::failed(llvm::LogicalResult) /scratch/hidetou/circt/llvm/llvm/include/llvm/Support/LogicalResult.h:71:58
#41 0x0000000000751288 main /scratch/hidetou/circt/tools/firtool/firtool.cpp:822:8
#42 0x00007f083b356d85 __libc_start_main (/lib64/libc.so.6+0x3ad85)
#43 0x000000000075030e _start (./build/bin/firtool+0x75030e)
Aborted
```

Ideally IR verifier should catch this

Start by running the supplied MLIR reproducer with firtool and inspect the failure in lib/Conversion/FIRRTLToHW/LowerToHW.cpp around setLowering. Then trace the FIRRTL IR verification path for module ports of type !firrtl.fstring. Done means the invalid port is rejected by the verifier with a diagnostic instead of reaching the lowering assertion.

Written by the indexing model from the issue text.