[llvm] [HEXAGON] [MachinePipeliner] Fix the DAG in case of dependent phis. (PR #135925)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj approved this pull request.

So, the code LGTM, but I think the PR description should be updated.

https://github.com/llvm/llvm-project/pull/135925