[llvm] [AMDGPU][GlobalISel] Fix pointer type handling in instruction selection (PR #181842)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

The types are being stripped away here, it shouldn't really matter if it's pointer or int. In this example is the problem really that the constant offset search looks through casts?

https://github.com/llvm/llvm-project/pull/181842