[llvm] [SPIR-V] Fix some GEP legalization (PR #150943)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> @Keenuts I've landed [022039e](https://github.com/llvm/llvm-project/commit/022039e4978991bd15263a78122166c0d3def8bb) to fix a warning from this PR. Thanks!

Oh thanks, nice catch!

https://github.com/llvm/llvm-project/pull/150943