[llvm] [AMDGPU] Guard RewriteMFMAFormStage recolor against unsafe def/use (PR #217396)

[Lucas Ramirez via llvm-commits]

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lucas-rami wrote:

Can you just re-use the slightly simpler test case from #214124? No need for control flow to trigger the issue. 

https://github.com/llvm/llvm-project/pull/217396