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

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

Please also check the CI failure. (From my experience, `swp-epilog-phi9.ll` is really fragile...)

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