[clang] [llvm] [CoroSplit] Don't go sub-word for suspend index (PR #221374)

[Weibo He via llvm-commits]

https://github.com/NewSigma approved this pull request.

LGTM. The CI failure seems unrelated. Since you're new to the project, I'll go ahead and land it directly.

https://github.com/llvm/llvm-project/pull/221374