[AArch64] Fix -Wunused-function of getLivePhysRegsUpTo in AArch64FrameLowering.cpp (NFC)

/llvm-project/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp:1428:13: error: unused function 'getLivePhysRegsUpTo' [-Werror,-Wunused-function]
static void getLivePhysRegsUpTo(MachineInstr &MI, const TargetRegisterInfo &TRI,
            ^
1 error generated.