Fix the clang compilation failure to handle all the values in a case statement for enum type value.

Signed-off-by: Andrew Fish
Reviewed-by: niruiyu

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12539 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Variable/Pei/Variable.c

@@ -383,6 +383,10 @@ GetVariableStore (
         }
       }
       break;
+
+    default:
+      ASSERT (FALSE);
+      break;
   }
 
   return VariableStoreHeader;