[llvm] [AMDGPU] Fix GFX11 sendmsg codes (PR #85299)

[Jay Foad via llvm-commits]

jayfoad wrote:

This is obviously right for GFX12, thanks. For GXF11 this code is not listed in the documentation I saw, but perhaps that was just a mistake in the doc.

https://github.com/llvm/llvm-project/pull/85299