[RISCV] Simplify some code. NFC

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -2340,8 +2340,7 @@ static SDValue lowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG,
 static SDValue splatPartsI64WithVL(const SDLoc &DL, MVT VT, SDValue Passthru,
                                    SDValue Lo, SDValue Hi, SDValue VL,
                                    SelectionDAG &DAG) {
-  bool HasPassthru = Passthru && !Passthru.isUndef();
-  if (!HasPassthru && !Passthru)
+  if (!Passthru)
     Passthru = DAG.getUNDEF(VT);
   if (isa<ConstantSDNode>(Lo) && isa<ConstantSDNode>(Hi)) {
     int32_t LoC = cast<ConstantSDNode>(Lo)->getSExtValue();