writeback: fix a typo in comment

Signed-off-by: Yan Hong <clouds.yan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 3e3422f..310972b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1034,7 +1034,7 @@
 	while (!kthread_freezable_should_stop(NULL)) {
 		/*
 		 * Remove own delayed wake-up timer, since we are already awake
-		 * and we'll take care of the preriodic write-back.
+		 * and we'll take care of the periodic write-back.
 		 */
 		del_timer(&wb->wakeup_timer);