block: NULL dereference on error path in __blkdev_get()

"disk" is always NULL when we goto out.  There was a check for this
before, but it was removed in 69e02c59a7d9 "block: Don't check events
while open is in progress".

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@carl>

fs/block_dev.c

@@ -1181,9 +1181,9 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
  out_unlock_bdev:
 	mutex_unlock(&bdev->bd_mutex);
 	disk_unblock_events(disk);
- out:
 	module_put(disk->fops->owner);
 	put_disk(disk);
+ out:
 	bdput(bdev);
 
 	return ret;