Fixed compiler warning

plugin/simple_password_check/simple_password_check.c

@@ -48,7 +48,8 @@ static int validate(MYSQL_LEX_STRING *username, MYSQL_LEX_STRING *password)
          others < min_others;
 }
 
-static void fix_min_length(MYSQL_THD thd, struct st_mysql_sys_var *var,
+static void fix_min_length(MYSQL_THD thd __attribute__((unused)),
+                           struct st_mysql_sys_var *var,
                            void *var_ptr, const void *save)
 {
   *((unsigned int *)var_ptr)= *((unsigned int *)save);