[llvm] AMDGPU: Use pointer types more consistently (PR #111651)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Oct 9, 9:22 AM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/111651).


https://github.com/llvm/llvm-project/pull/111651