[llvm] [AMDGPU][SIInsertWaitcnts][NFC] Use loop to set Wait entries (PR #178764)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Please note that the original code was skipping STORE_CNT but this one is not.

That should be fine, because frmo looking at `setForceEmitWaitcnt`, `ForceEmitWaitcnt[STORE_CNT]` will never be set to true anyway.

https://github.com/llvm/llvm-project/pull/178764