[LV] Drop unneeded use of getVPSingleValue (NFC).

VPReductionPHIRecipe inherits from VPValue, so there's no need to call
getVPSingleValue.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -4355,7 +4355,7 @@ void InnerLoopVectorizer::fixReduction(VPReductionPHIRecipe *PhiR,
               RdxDesc.getOpcode(), PhiTy,
               TargetTransformInfo::ReductionFlags())) {
         auto *VecRdxPhi =
-            cast<PHINode>(State.get(PhiR->getVPSingleValue(), Part));
+            cast<PHINode>(State.get(PhiR, Part));
         VecRdxPhi->setIncomingValueForBlock(
             LI->getLoopFor(LoopVectorBody)->getLoopLatch(), Sel);
       }