[clang] [NFC] [clang][SPIR-V] Use AMDGPU prefix to avoid confusion (PR #96962)

[Alex Voicu via cfe-commits]

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

LTGM, thanks! Also, apologies for any inconvenience caused.

https://github.com/llvm/llvm-project/pull/96962