bdi: Drop 'parent' argument from bdi_register[_va]()

Drop 'parent' argument of bdi_register() and bdi_register_va().  It is
always NULL.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/mtd/mtdcore.c

@@ -1782,7 +1782,7 @@ static struct backing_dev_info * __init mtd_bdi_init(char *name)
 	 * We put '-0' suffix to the name to get the same name format as we
 	 * used to get. Since this is called only once, we get a unique name. 
 	 */
-	ret = bdi_register(bdi, NULL, "%.28s-0", name);
+	ret = bdi_register(bdi, "%.28s-0", name);
 	if (ret)
 		bdi_put(bdi);