ArmPkg: ArmLib: Update function to match header file

Update function implementation to match interface definition. The return
should be bound to 0xffff0000, which is guaranteed to be a UINT32.

Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Sami Mujawar <sami.mujawar@arm.com>

Signed-off-by: Kun Qin <kun.qin@microsoft.com>

ArmPkg/Library/ArmLib/ArmLib.c

@@ -71,15 +71,15 @@ ArmInstructionCacheLineLength (
   return 4 << (ArmCacheInfo () & 0xf); // CTR_EL0.IminLine
 }
 
-UINTN
+UINT32
 EFIAPI
 ArmCacheWritebackGranule (
   VOID
   )
 {
-  UINTN  CWG;
+  UINT32  CWG;
 
-  CWG = (ArmCacheInfo () >> 24) & 0xf; // CTR_EL0.CWG
+  CWG = (UINT32)((ArmCacheInfo () >> 24) & 0xf); // CTR_EL0.CWG
 
   if (CWG == 0) {
     return SIZE_2KB;