[InferAddressSpaces] can't infer load's value address space

```c
__global__ void globalmem_flat_ptr_with_global(int** a, int* b) {
int* ptra = *a;
int v = ptra[threadIdx.x];
b[threadIdx.x] = v;
}
```
nvcc：
```asm
ld.global.u32 %r2, [%rd8];
add.s64 %rd9, %rd3, %rd7;
st.global.u32 [%rd9], %r2;
ret;
```

clang：
```asm
ld.b32 %r2, [%rd7];
add.s64 %rd8, %rd4, %rd6;
st.global.b32 [%rd8], %r2;
ret;
```

https://godbolt.org/z/qG5qbcbq6