nilfs2: Convert to properly refcounting bdi

Similarly to set_bdev_super() NILFS2 just used block device reference to
bdi. Convert it to properly getting bdi reference. The reference will
get automatically dropped on superblock destruction.

CC: [e-mail]
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>
Acked-by: Ryusuke Konishi <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/nilfs2/super.c

···
 	sb->s_time_gran = 1;
 	sb->s_max_links = NILFS_LINK_MAX;
 
-	sb->s_bdi = bdev_get_queue(sb->s_bdev)->backing_dev_info;
+	sb->s_bdi = bdi_get(sb->s_bdev->bd_bdi);
+	sb->s_iflags |= SB_I_DYNBDI;
 
 	err = load_nilfs(nilfs, sb);
 	if (err)