[llvm] [AMDGPU] Fix RewriteMFMAFormSchedStage (PR #194887)

[via llvm-commits]

xgxanq wrote:

@arsenm  hi, matt. I can't create branches directly from llvm-project. As for stacked PRs, I can't implement that for now. So I forked two separate branches in my forked repo, and linked them together in the PR description. the only tests PR is https://github.com/llvm/llvm-project/pull/193429 , the old one.

https://github.com/llvm/llvm-project/pull/194887