[SelectionDAGBuilder][NFC] Pass LHSTy to getShiftAmountTy rather than RHSTy

r126518 introduced a a type parameter to the getShiftAmountTy target hook. It 
produces the type of the shift (RHSTy), parameterised by the type of the value 
being shifted (LHSTy). SelectionDAGBuilder::visitShift passed RHSTy rather 
than LHSTy and this patch corrects this. The change is a no-op because in LLVM 
IR the LHS and RHS types for a shift must be equal anyway.

llvm-svn: 343955

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -2827,7 +2827,7 @@ void SelectionDAGBuilder::visitShift(const User &I, unsigned Opcode) {
   SDValue Op2 = getValue(I.getOperand(1));
 
   EVT ShiftTy = DAG.getTargetLoweringInfo().getShiftAmountTy(
-      Op2.getValueType(), DAG.getDataLayout());
+      Op1.getValueType(), DAG.getDataLayout());
 
   // Coerce the shift amount to the right type if we can.
   if (!I.getType()->isVectorTy() && Op2.getValueType() != ShiftTy) {