bcache: cached_dev_free needs to put the sb page

Same as cache device, the buffer page needs to be put while
freeing cached_dev.  Otherwise a page would be leaked every
time a cached_dev is stopped.
Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/super.c

@@ -1275,6 +1275,9 @@ static void cached_dev_free(struct closure *cl)
 
 	mutex_unlock(&bch_register_lock);
 
+	if (dc->sb_bio.bi_inline_vecs[0].bv_page)
+		put_page(bio_first_page_all(&dc->sb_bio));
+
 	if (!IS_ERR_OR_NULL(dc->bdev))
 		blkdev_put(dc->bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);