[llvm] [NFC][AMDGPU] Assert no bad shift operations will happen (PR #108416)

[Georgi Mirazchiyski via llvm-commits]

GeorgeWeb wrote:

I am a silly, `Mask` is `int64_t`, and `has_single_bit` only works on unsigned integers.
@jplehr Is the procedure to revert this in main and resubmit the fixed version or I just push a follow-up fix? Apologies!

https://github.com/llvm/llvm-project/pull/108416