[llvm] [NFC][SPIRV] Misc code cleanup in SPIRV Target (PR #133764)

[Alexey Bader via llvm-commits]

bader wrote:

@jurahul, thanks. All changes look reasonable to me, but I would prefer @VyacheslavLevytskyy or @Keenuts to approve before merging.

https://github.com/llvm/llvm-project/pull/133764