[llvm] [SPIR-V] Guard against infinite loop in decorateUsesAsNonUniform (PR #208224)

[Dmitry Sidorov via llvm-commits]

https://github.com/MrSidims commented:

the patch makes sense, but I can't vouch for SPIR-V correctness and I'm not HLSL expert.

https://github.com/llvm/llvm-project/pull/208224