md: md_stop_writes() should always freeze recovery.

__md_stop_writes() will currently sometimes freeze recovery.
So any caller must be ready for that to happen, and indeed they are.

However if __md_stop_writes() doesn't freeze_recovery, then
a recovery could start before mddev_suspend() is called, which
could be awkward.  This can particularly cause problems or dm-raid.

So change __md_stop_writes() to always freeze recovery.  This is safe
and more predicatable.
Reported-by: Brassow Jonathan <jbrassow@redhat.com>
Tested-by: Brassow Jonathan <jbrassow@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -5277,8 +5277,8 @@ static void md_clean(struct mddev *mddev)
 
 static void __md_stop_writes(struct mddev *mddev)
 {
-	if (mddev->sync_thread) {
 	set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
+	if (mddev->sync_thread) {
 		set_bit(MD_RECOVERY_INTR, &mddev->recovery);
 		md_reap_sync_thread(mddev);
 	}