[llvm] [AArch64][MachineCombiner] Fix setting reg state for gather lane pattern (PR #149703)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

I think this is OK. Replacing the auto's, whilst a good change, makes the differences a little more difficult to follow. It might be worth having a test where the kill flags are different between different instructions too, to show that the right ones are removed.

As there is another issue it might be better to revert the original and recommit these together with a fix.

https://github.com/llvm/llvm-project/pull/149703