[AArch64] Remove an unnecessary cast (NFC)

getRegisterInfo() already returns const AArch64RegisterInfo *.

Author: kazutakahirata

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -731,8 +731,7 @@ void AArch64FrameLowering::resetCFIToInitialState(
 
   MachineFunction &MF = *MBB.getParent();
   const auto &Subtarget = MF.getSubtarget<AArch64Subtarget>();
-  const auto &TRI =
-      static_cast<const AArch64RegisterInfo &>(*Subtarget.getRegisterInfo());
+  const auto &TRI = *Subtarget.getRegisterInfo();
   const auto &MFI = *MF.getInfo<AArch64FunctionInfo>();
 
   CFIInstBuilder CFIBuilder(MBB, MBB.begin(), MachineInstr::NoFlags);