[llvm] [AVR] Temp fix for getPostIndexedAddressParts() (PR #145040)

[Ben Shi via llvm-commits]

benshi001 wrote:

> @Benshi Thanks for the review.
> 
> What do you mean with "the generated .ll files have slight difference"? Which files are you comparing? Changing `if 1` to `if 0` in the test program and comparing the .ll or something else?

I was comparing your test program 
```c++
#define PA      0x1 // Bad
//#define PA    0x2 // Good

volatile char *const PORT = (char *const) PA;

extern void nil(short);

void bug()
{
  short s= 0;
 
  while (1) {
    s++;
    *PORT = *PORT | 0x80;
    nil((s & 0xF) + 1);
  }
}
```

https://github.com/llvm/llvm-project/pull/145040