[AArch64] Fix -Wunused-variable in AArch64ISelLowering.cpp (NFC)

llvm-project/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp:27379:19:
error: unused variable 'CID' [-Werror,-Wunused-variable]
  ConstantSDNode *CID = cast<ConstantSDNode>(IntID.getNode());
                  ^
1 error generated.