[InstCombine] Use replaceOperand() in non zero phi transform

To make sure the old operand gets DCEd.

NFC apart from worklist order changes.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

@@ -1203,7 +1203,7 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
             NonZeroConst = GetAnyNonZeroConstInt(PN);
 
           if (NonZeroConst != VA) {
-            PN.setIncomingValue(i, NonZeroConst);
+            replaceOperand(PN, i, NonZeroConst);
             MadeChange = true;
           }
         }