Fix -Wimplicit-fallthrough warnings (no functional change)

sql/sql_table.cc

@@ -1174,6 +1174,7 @@ static int execute_ddl_log_action(THD *thd, DDL_LOG_ENTRY *ddl_log_entry)
         action in the log entry by stepping up the phase.
       */
     }
+    /* fall through */
     case DDL_LOG_RENAME_ACTION:
     {
       error= TRUE;