brd: fix name argument of unregister_blkdev()

The name of brd block device is "ramdisk", it's not "brd".
(The block device is registered by register_blkdev(RAMDISK_MAJOR, "ramdisk")
So it should be unregistered by unregister_blkdev(RAMDISK_MAJOR, "ramdisk")

Signed-off-by: Akinobu Mita <[e-mail]>
Acked-by: Nick Piggin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/block/brd.c

···
 		list_del(&brd->brd_list);
 		brd_free(brd);
 	}
+	unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
 
-	unregister_blkdev(RAMDISK_MAJOR, "brd");
 	return -ENOMEM;
 }