[llvm] [CodeGen] Simplify updateLiveIn in MachineSink (PR #79831)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Should this add the test case from VE?

It would be nice to have a VE test case but the only one I've seen so far is https://github.com/llvm/llvm-project/compare/main...kaz7:llvm-project:computeregunitlanemasks-test which is specific to the TableGen fix (#79462) - it is no use for this fix. @kaz7

https://github.com/llvm/llvm-project/pull/79831