[AArch64] Use spill size when calculating SVE callee saves size (NFC)

This is an NFC right now, as currently, all SVE register and spill sizes
are the same, but the spill size is the correct size to use here.

Author: MacDue

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -3795,14 +3795,15 @@ void AArch64FrameLowering::determineCalleeSaves(MachineFunction &MF,
   unsigned CSStackSize = 0;
   unsigned SVECSStackSize = 0;
   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
-  const MachineRegisterInfo &MRI = MF.getRegInfo();
   for (unsigned Reg : SavedRegs.set_bits()) {
-    auto RegSize = TRI->getRegSizeInBits(Reg, MRI) / 8;
+    auto *RC = TRI->getMinimalPhysRegClass(Reg);
+    assert(RC && "expected register class!");
+    auto SpillSize = TRI->getSpillSize(*RC);
     if (AArch64::PPRRegClass.contains(Reg) ||
         AArch64::ZPRRegClass.contains(Reg))
-      SVECSStackSize += RegSize;
+      SVECSStackSize += SpillSize;
     else
-      CSStackSize += RegSize;
+      CSStackSize += SpillSize;
   }
 
   // Increase the callee-saved stack size if the function has streaming mode