[llvm] [SPIRV] Fix warning in SPIRVMergeRegionExitTargets.cpp (PR #95283)

[Nathan Gauër via llvm-commits]

https://github.com/Keenuts approved this pull request.

Thanks! 
How did you get this warning? (Don't have it on my local build)

https://github.com/llvm/llvm-project/pull/95283