MdeModulePkg/VarCheckHiiLib: don't return success for invalid input

The doxygen comment for VarCheckHiiLibReceiveHiiBinHandler says that
EFI_INVALID_PARAMETER should be returned if either of CommBuffer or
CommBufferSize is NULL, but the test results in an early return of
EFI_SUCCESS.

Update the code to match the documentation.

Signed-off-by: Leif Lindholm <leif.lindholm@oss.qualcomm.com>

MdeModulePkg/Library/VarCheckHiiLib/VarCheckHiiLibStandaloneMm.c

@@ -58,7 +58,7 @@ VarCheckHiiLibReceiveHiiBinHandler (
   // If input is invalid, stop processing this SMI
   //
   if ((CommBuffer == NULL) || (CommBufferSize == NULL)) {
-    return EFI_SUCCESS;
+    return EFI_INVALID_PARAMETER;
   }
 
   mMmReceivedVarCheckHiiBinSize = *CommBufferSize;