[clang] [coroutine] Fix type of an ImplicitParamDecl used in generateAwaitSuspendWrapper (PR #87134)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 commented:

The change itself looks good to me. It will be better if we can have a reduced test case.

https://github.com/llvm/llvm-project/pull/87134