[MTD] Always initialise mutex in new mtd_blktrans_dev.

We were only initialising the mutex in the case where the new device was
automatically allocated the highest minor number. If the caller
specified a minor number, or if it filled in a free slot which was made
by a previous device deregistering, the mutex wouldn't get initialised
when we jumped out of the loop.

Reported by Monte Copeland <catboat@texas.net>
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>

drivers/mtd/mtd_blkdevs.c

@@ -248,9 +248,9 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 		return -EBUSY;
 	}
 
-	mutex_init(&new->lock);
 	list_add_tail(&new->list, &tr->devs);
  added:
+	mutex_init(&new->lock);
 	if (!tr->writesect)
 		new->readonly = 1;