[SLP][NFC] Make calculateTreeCostAndTrimNonProfitable compatible
with processBuildVector, NFC
processBuildVector adjusts the scalars to match the entry vector factor,
while calculateTreeCostAndTrimNonProfitable does not. Sync the behovior
to avoid potential issues. Currently it does not affect the cost
estimations, so it is NFC.
Reviewers:
Pull Request: https://github.com/llvm/llvm-project/pull/191905