[llvm] [AMDGPU] Handle phys regs in flat_scratch_base_hi operand check (PR #170395)

[Shilei Tian via llvm-commits]

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

`MIR`'s doesn't account for phys reg while `RI`'s does? These interfaces are confusing…

https://github.com/llvm/llvm-project/pull/170395