[llvm] [IR] Fix llvm.powi intrinsic decl (PR #216160)

[Kamlesh Kumar via llvm-commits]

kamleshbhalui wrote:

> A correctness issue was identified by [llvm-hackme](https://github.com/dtcxzyw/llvm-hackme). Please see the [issue comment](https://github.com/llvm/llvm-project/pull/216160#issuecomment-5286056099) for details.

thanks, this is great, fixed it.

https://github.com/llvm/llvm-project/pull/216160