mtd: add add_disk() error handling

We never checked for errors on add_disk() as this function
returned void. Now that this is fixed, use the shiny new
error handling.

Acked-by: Miquel Raynal <[e-mail]>
Signed-off-by: Luis Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/mtd/mtd_blkdevs.c

···
 	if (new->readonly)
 		set_disk_ro(gd, 1);
 
-	device_add_disk(&new->mtd->dev, gd, NULL);
+	ret = device_add_disk(&new->mtd->dev, gd, NULL);
+	if (ret)
+		goto out_cleanup_disk;
 
 	if (new->disk_attributes) {
 		ret = sysfs_create_group(&disk_to_dev(gd)->kobj,
···
 	}
 	return 0;
 
+out_cleanup_disk:
+	blk_cleanup_disk(new->disk);
 out_free_tag_set:
 	blk_mq_free_tag_set(new->tag_set);
 out_kfree_tag_set: