[llvm] [AMDGPU][Legalizer] Widen i16 G_SEXT_INREG (PR #131308)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

### Merge activity

* **May 7, 4:20 AM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/131308).


https://github.com/llvm/llvm-project/pull/131308