ScratchVar load before store conflicting with Subroutines.

### Subject of the issue

Compiler checks for load before store do not work as expected when Subroutines that takes ScratchVar as arguments are used.

### Steps to reproduce

```python
from pyteal import *

def example():
var = ScratchVar(TealType.uint64)

@Subroutine(TealType.none)
def sub(x: ScratchVar):
return x.store(Int(0))

return Seq([
sub(var),
Pop(var.load()),
Approve()
])

if __name__ == '__main__':
print(compileTeal(example(), mode=Mode.Application, version=6))

```

### Expected behaviour

Contract can compile correctly

### Actual behaviour

`pyteal.TealCompileError: Scratch slot load occurs before store`