[llvm] [AMDGPU] Simplify getIns64. NFCI. (PR #139981)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

> Interesting... Failure only happens in a debug build and it is not an assert...

OK, it did not factor v_nop w/o any operands. Fixed.

https://github.com/llvm/llvm-project/pull/139981