[llvm] [LLVM][CodeGen] Fix register lane liveness tracking in RegisterPressure (PR #88892)

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

> LGTM. Just double checking, this commit is already exercised by existing tests, right? Otherwise, could you add a test?

Yes.  This assertion, when enabled without this fix, causes lots of existing AMDGPU tests to fail.

https://github.com/llvm/llvm-project/pull/88892