[llvm] [VPlan] Return partial reduction cost only for VPPartialReductionRecipe (NFC) (PR #167846)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

It looks like this can just be folded into https://github.com/llvm/llvm-project/pull/147513, which should land soon, so it's probably not worth doing this as intermediate step and it can wait until https://github.com/llvm/llvm-project/pull/147513 lands

https://github.com/llvm/llvm-project/pull/167846