writeback: use schedule_timeout_interruptible()

Gets rid of a manual set_current_state().

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 55f0d4e..3475775 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -884,8 +884,7 @@
 		}
 
 		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
-		set_current_state(TASK_INTERRUPTIBLE);
-		schedule_timeout(wait_jiffies);
+		schedule_timeout_interruptible(wait_jiffies);
 		try_to_freeze();
 	}