dm: use dm_target_offset macro

Use new dm_target_offset() macro to avoid most references to ti->begin
in dm targets.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c
index 8520528..a91049e 100644
--- a/drivers/md/dm-delay.c
+++ b/drivers/md/dm-delay.c
@@ -281,14 +281,13 @@
 		bio->bi_bdev = dc->dev_write->bdev;
 		if (bio_sectors(bio))
 			bio->bi_sector = dc->start_write +
-					 (bio->bi_sector - ti->begin);
+					 dm_target_offset(ti, bio->bi_sector);
 
 		return delay_bio(dc, dc->write_delay, bio);
 	}
 
 	bio->bi_bdev = dc->dev_read->bdev;
-	bio->bi_sector = dc->start_read +
-			 (bio->bi_sector - ti->begin);
+	bio->bi_sector = dc->start_read + dm_target_offset(ti, bio->bi_sector);
 
 	return delay_bio(dc, dc->read_delay, bio);
 }