MD: change the parameter of md thread

Change the thread parameter, so the thread can carry extra info. Next patch
will use it.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 05c557e..55ccf47 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2294,8 +2294,9 @@
 	}
 }
 
-static void raid1d(struct mddev *mddev)
+static void raid1d(struct md_thread *thread)
 {
+	struct mddev *mddev = thread->mddev;
 	struct r1bio *r1_bio;
 	unsigned long flags;
 	struct r1conf *conf = mddev->private;