[llvm] AMDGPU: Use default shouldRewriteCopySrc (PR #125535)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Feb 7, 12:29 AM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/125535).


https://github.com/llvm/llvm-project/pull/125535