[ARC] Update code after removal of Register::isStackSlot. NFC

Author: topperc

llvm/lib/Target/ARC/ARCOptAddrMode.cpp

@@ -216,7 +216,7 @@ MachineInstr *ARCOptAddrMode::tryToCombine(MachineInstr &Ldst) {
   }
 
   Register B = Base.getReg();
-  if (Register::isStackSlot(B) || !Register::isVirtualRegister(B)) {
+  if (B.isStackSlot() || !B.isVirtual()) {
     LLVM_DEBUG(dbgs() << "[ABAW] Base is not VReg\n");
     return nullptr;
   }