[RISCV] Remove unnecessary APInt copy. NFC

getAPIntValue returns a const APInt& so keep it as a reference.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -2009,7 +2009,7 @@ bool RISCVTargetLowering::isDesirableToCommuteWithShift(
     auto *C1 = dyn_cast<ConstantSDNode>(N0->getOperand(1));
     auto *C2 = dyn_cast<ConstantSDNode>(N->getOperand(1));
     if (C1 && C2) {
-      APInt C1Int = C1->getAPIntValue();
+      const APInt &C1Int = C1->getAPIntValue();
       APInt ShiftedC1Int = C1Int << C2->getAPIntValue();
 
       // We can materialise `c1 << c2` into an add immediate, so it's "free",