[llvm] AMDGPU: Fix assert when multi operands to update after folding imm (PR #148205)

[Shilei Tian via llvm-commits]

shiltian wrote:

I'm not sure if the MIR test can be trimmed further (and I hope it can), but if @arsenm is happy with it, I'm totally fine with it.

https://github.com/llvm/llvm-project/pull/148205