[llvm] [FastISel][X86] Use getTypeForExtReturn in GetReturnInfo. (PR #80803)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Given DAGIsel doesn't do zeroext on callee and both do zeroext in caller https://godbolt.org/z/e4qf3Mdrn. I think we are safe to go with this patch.

This sounds broken though 

https://github.com/llvm/llvm-project/pull/80803