[SLP] nullptr'ize initial value in findBuildAggregate(), NFC.

Initial value of V is sett nullptr, as it is not used.

llvm-svn: 295642

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -4614,7 +4614,7 @@ static bool findBuildVector(InsertElementInst *FirstInsertElem,
 static bool findBuildAggregate(InsertValueInst *IV,
                                SmallVectorImpl<Value *> &BuildVector,
                                SmallVectorImpl<Value *> &BuildVectorOpds) {
-  Value *V = IV;
+  Value *V = nullptr;
   do {
     BuildVector.push_back(IV);
     BuildVectorOpds.push_back(IV->getInsertedValueOperand());