block: convert to bio_first_bvec_all & bio_first_page_all

This patch converts to bio_first_bvec_all() & bio_first_page_all() for
retrieving the 1st bvec/page, and prepares for supporting multipage bvec.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/mm/page_io.c b/mm/page_io.c
index e93f1a4..b41cf96 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -50,7 +50,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
 
 void end_swap_bio_write(struct bio *bio)
 {
-	struct page *page = bio->bi_io_vec[0].bv_page;
+	struct page *page = bio_first_page_all(bio);
 
 	if (bio->bi_status) {
 		SetPageError(page);
@@ -122,7 +122,7 @@ static void swap_slot_free_notify(struct page *page)
 
 static void end_swap_bio_read(struct bio *bio)
 {
-	struct page *page = bio->bi_io_vec[0].bv_page;
+	struct page *page = bio_first_page_all(bio);
 	struct task_struct *waiter = bio->bi_private;
 
 	if (bio->bi_status) {