rbd: fix spelling mistake: "reregisteration" -> "reregistration"

Trivial fix to spelling mistake in rdb_warn message text.
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

drivers/block/rbd.c

@@ -3479,7 +3479,7 @@ static void rbd_reregister_watch(struct work_struct *work)
 
 	ret = rbd_dev_refresh(rbd_dev);
 	if (ret)
-		rbd_warn(rbd_dev, "reregisteration refresh failed: %d", ret);
+		rbd_warn(rbd_dev, "reregistration refresh failed: %d", ret);
 }
 
 /*