[AArch64] Avoid warning about comparison of different signedness. NFC. (#159337)

This fixes the following warning when compiled with GCC:

    ../lib/Target/AArch64/AArch64ISelLowering.cpp: In function ‘bool shouldLowerTailCallStackArg(const llvm::MachineFunction&, const llvm::CCValAssign&, llvm::SDValue, llvm::ISD::ArgFlagsTy, int)’:
    ../lib/Target/AArch64/AArch64ISelLowering.cpp:9310: warning: comparison of integer expressions of different signedness: ‘uint64_t’ {aka ‘long unsigned int’} and ‘int64_t’ {aka ‘long int’} [-Wsign-compare]
     9310 |       if (SizeInBits / 8 != MFI.getObjectSize(FI))
          |

Author: mstorsjo

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -9306,7 +9306,7 @@ static bool shouldLowerTailCallStackArg(const MachineFunction &MF,
       if (CallOffset != MFI.getObjectOffset(FI))
         return true;
       uint64_t SizeInBits = LoadNode->getMemoryVT().getFixedSizeInBits();
-      if (SizeInBits / 8 != MFI.getObjectSize(FI))
+      if (SizeInBits / 8 != static_cast<uint64_t>(MFI.getObjectSize(FI)))
         return true;
       return false;
     }