[llvm] [AMDGPU] Make `getAssumedAddrSpace` return AS1 for pointer kernel arguments (PR #137488)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I've been thinking we should probably remove InferAddressSpaces from the codegen pass pipeline, it would avoid most of the test diffs here 

https://github.com/llvm/llvm-project/pull/137488