md: use sysfs_notify_dirent to notify changes to md/array_state

Now that we have sysfs_notify_dirent, use it to notify changes
to md/array_state.
As sysfs_notify_dirent can be called in atomic context, we can
remove the delayed notify and the MD_NOTIFY_ARRAY_STATE flag.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index c200b9a..b16ad86 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -128,7 +128,6 @@
 #define MD_CHANGE_DEVS	0	/* Some device status has changed */
 #define MD_CHANGE_CLEAN 1	/* transition to or from 'clean' */
 #define MD_CHANGE_PENDING 2	/* superblock update in progress */
-#define MD_NOTIFY_ARRAY_STATE 3	/* atomic context wants to notify userspace */
 
 	int				ro;
 
@@ -239,6 +238,10 @@
 	sector_t			resync_max;	/* resync should pause
 							 * when it gets here */
 
+	struct sysfs_dirent		*sysfs_state;	/* handle for 'array_state'
+							 * file in sysfs.
+							 */
+
 	spinlock_t			write_lock;
 	wait_queue_head_t		sb_wait;	/* for waiting on superblock updates */
 	atomic_t			pending_writes;	/* number of active superblock writes */