md/raid5: Fix spelling mistakes in comments

Fix spelling of 'waitting' in comments.

Signed-off-by: XU pengfei <xupengfei@nfschina.com>
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/raid5-cache.c

@@ -1327,9 +1327,9 @@ static void r5l_write_super_and_discard_space(struct r5l_log *log,
 	 * superblock is updated to new log tail. Updating superblock (either
 	 * directly call md_update_sb() or depend on md thread) must hold
 	 * reconfig mutex. On the other hand, raid5_quiesce is called with
-	 * reconfig_mutex hold. The first step of raid5_quiesce() is waitting
-	 * for all IO finish, hence waitting for reclaim thread, while reclaim
-	 * thread is calling this function and waitting for reconfig mutex. So
+	 * reconfig_mutex hold. The first step of raid5_quiesce() is waiting
+	 * for all IO finish, hence waiting for reclaim thread, while reclaim
+	 * thread is calling this function and waiting for reconfig mutex. So
 	 * there is a deadlock. We workaround this issue with a trylock.
 	 * FIXME: we could miss discard if we can't take reconfig mutex
 	 */