[X86] Fix a mistake in the X86ISelDAGToDAG.cpp code for MUL8r/IMUL8r.

I think this code is unreachable due to some promotions that occur elsewhere. I'll look into that to be sure, but for now I thought I should at least fix the obvious typo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316840 91177308-0d34-0410-b5e6-96231b3b80d8

Author: topperc

lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -2728,7 +2728,7 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
       // Get the low part if needed. Don't use getCopyFromReg for aliasing
       // registers.
       if (!SDValue(Node, 0).use_empty())
-        ReplaceUses(SDValue(Node, 1),
+        ReplaceUses(SDValue(Node, 0),
           CurDAG->getTargetExtractSubreg(X86::sub_8bit, dl, MVT::i8, Result));
 
       // Shift AX down 8 bits.