Use the simpler mechanism attached to major_name to allocate a md device
when a currently unregistered minor is accessed.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Acked-by: NSong Liu <song@kernel.org>
Signed-off-by: NJens Axboe <axboe@kernel.dk>