drbd: fix memory leak

We forgot to free the disk_conf,
so for each attach/detach cycle we leaked 336 bytes.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_main.c

@@ -2819,6 +2819,7 @@ void drbd_free_bc(struct drbd_backing_dev *ldev)
 	blkdev_put(ldev->backing_bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
 	blkdev_put(ldev->md_bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
 
+	kfree(ldev->disk_conf);
 	kfree(ldev);
 }