[llvm] PeepholeOpt: Do not add subregister indexes to reg_sequence operands (PR #124111)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Jan 30, 8:37 AM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/124111).


https://github.com/llvm/llvm-project/pull/124111