blk-throttle: Remove a meaningless parameter for throtl_downgrade_state()

The throtl_downgrade_state() is always used to change to LIMIT_LOW
limitation, thus remove the latter meaningless parameter which
indicates the limitation index.
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-throttle.c

@@ -1970,7 +1970,7 @@ static void throtl_upgrade_state(struct throtl_data *td)
 	queue_work(kthrotld_workqueue, &td->dispatch_work);
 }
 
-static void throtl_downgrade_state(struct throtl_data *td, int new)
+static void throtl_downgrade_state(struct throtl_data *td)
 {
 	td->scale /= 2;
 
@@ -1980,7 +1980,7 @@ static void throtl_downgrade_state(struct throtl_data *td, int new)
 		return;
 	}
 
-	td->limit_index = new;
+	td->limit_index = LIMIT_LOW;
 	td->low_downgrade_time = jiffies;
 }
 
@@ -2067,7 +2067,7 @@ static void throtl_downgrade_check(struct throtl_grp *tg)
 	 * cgroups
 	 */
 	if (throtl_hierarchy_can_downgrade(tg))
-		throtl_downgrade_state(tg->td, LIMIT_LOW);
+		throtl_downgrade_state(tg->td);
 
 	tg->last_bytes_disp[READ] = 0;
 	tg->last_bytes_disp[WRITE] = 0;