[llvm] [SPIRV] Fix failing assertion in SPIRVAsmPrinter (PR #166909)

[Juan Manuel Martinez Caamaño via llvm-commits]

jmmartinez wrote:

I've added a last commit where I refactor a redundant condition and rename ConstZero into ConstZeroInt32, but if it's not relevant I can remove it (it polutes the PR a bit and is an unrelated NFC).

https://github.com/llvm/llvm-project/pull/166909