[RISCV][NFC] Use defined variable instead some code.

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

if (N0.getOpcode() != ISD::AND || !N0.hasOneUse() ||
       N0.getConstantOperandVal(1) != UINT64_C(0xffffffff))
     return SDValue();
 
   // Looking for an equality compare.
   ISD::CondCode Cond = cast<CondCodeSDNode>(N->getOperand(2))->get();
   if (!isIntEqualitySetCC(Cond))
     return SDValue();
 
-  const APInt &C1 = cast<ConstantSDNode>(N1)->getAPIntValue();
+  const APInt &C1 = N1C->getAPIntValue();
 
   SDLoc dl(N);
   // If the constant is larger than 2^32 - 1 it is impossible for both sides
   // to be equal.
   if (C1.getActiveBits() > 32)
     return DAG.getBoolConstant(Cond == ISD::SETNE, dl, VT, OpVT);
 
   SDValue SExtOp = DAG.getNode(ISD::SIGN_EXTEND_INREG, N, OpVT,