block: switch bios to blk_status_t

Replace bi_error with a new bi_status to allow for a clear conversion.
Note that device mapper overloaded bi_error with a private value, which
we'll have to keep arround at least for now and thus propagate to a
proper blk_status_t value.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/mm/page_io.c b/mm/page_io.c
index 23f6d0d..2da71e6 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -45,7 +45,7 @@ void end_swap_bio_write(struct bio *bio)
 {
 	struct page *page = bio->bi_io_vec[0].bv_page;
 
-	if (bio->bi_error) {
+	if (bio->bi_status) {
 		SetPageError(page);
 		/*
 		 * We failed to write the page out to swap-space.
@@ -118,7 +118,7 @@ static void end_swap_bio_read(struct bio *bio)
 {
 	struct page *page = bio->bi_io_vec[0].bv_page;
 
-	if (bio->bi_error) {
+	if (bio->bi_status) {
 		SetPageError(page);
 		ClearPageUptodate(page);
 		pr_alert("Read-error on swap-device (%u:%u:%llu)\n",