[llvm] [RegisterCoalescer] Fix issue in the RegisterCoalescer. (PR #96839)

[Quentin Colombet via llvm-commits]

qcolombet wrote:

> Title should be descriptive of what the problem is, not a vague "fix issue"

+1 on that.

Could you describe what was the issue and how this patch fixes it?

https://github.com/llvm/llvm-project/pull/96839