[clang] [llvm] [llvm][OpenMP][SPIRV] Fix assertion for GPU reductions (PR #194879)

[Alex Duran via cfe-commits]

adurang wrote:

> As mentioned, we need a test. We also shouldn't mention SPRIV in the comment, it's an AS thing that's sufficient.

Done, I hope :)

https://github.com/llvm/llvm-project/pull/194879