[llvm] [AMDGPU][True16] fix a bug in codeGen causing e64 with wrong vgpr type to shrink (PR #102942)

[Brox Chen via llvm-commits]

broxigarchen wrote:

> Needs test

Added a small test to verify and to prevent furture failure. Should be expanded when more true16 and fake16 instructions are supported

https://github.com/llvm/llvm-project/pull/102942