block: export bio_free_pages to other modules

bio_free_pages is introduced in commit 1dfa0f68c040
("block: add a helper to free bio bounce buffer pages"),
we can reuse the func in other modules after it was
imported.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@fb.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
index c28df164..333a1e5 100644
--- a/drivers/md/bcache/debug.c
+++ b/drivers/md/bcache/debug.c
@@ -107,9 +107,8 @@
 {
 	char name[BDEVNAME_SIZE];
 	struct bio *check;
-	struct bio_vec bv, *bv2;
+	struct bio_vec bv;
 	struct bvec_iter iter;
-	int i;
 
 	check = bio_clone(bio, GFP_NOIO);
 	if (!check)
@@ -136,8 +135,7 @@
 		kunmap_atomic(p1);
 	}
 
-	bio_for_each_segment_all(bv2, check, i)
-		__free_page(bv2->bv_page);
+	bio_free_pages(check);
 out_put:
 	bio_put(check);
 }