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/fs/buffer.c b/fs/buffer.c
index 161be58..306b720 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3038,7 +3038,7 @@ static void end_bio_bh_io_sync(struct bio *bio)
 	if (unlikely(bio_flagged(bio, BIO_QUIET)))
 		set_bit(BH_Quiet, &bh->b_state);
 
-	bh->b_end_io(bh, !bio->bi_error);
+	bh->b_end_io(bh, !bio->bi_status);
 	bio_put(bio);
 }