[AArch64] Silent an unused-variable warning (NFC)
/llvm-project/llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp:1042:11:
error: unused variable 'TRI' [-Werror,-Wunused-variable]
auto *TRI = MBB.getParent()->getSubtarget().getRegisterInfo();
^
1 error generated.
