dm thin: fixup for lack of bio_inc_remaining in 4.1

drivers/md/dm-thin.c

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index b6b3b82..2086eb6 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1533,18 +1533,6 @@
 		pool->process_prepared_discard(m);
 }
 
-/*
- * FIXME: DM local hack to defer parent bios's end_io until we
- * _know_ all chained sub range discard bios have completed.
- * Will go away once late bio splitting lands upstream!
- */
-static inline void __bio_inc_remaining(struct bio *bio)
-{
-	bio->bi_flags |= (1 << BIO_CHAIN);
-	smp_mb__before_atomic();
-	atomic_inc(&bio->__bi_remaining);
-}
-
 static void break_up_discard_bio(struct thin_c *tc, dm_block_t begin, dm_block_t end,
 				 struct bio *bio)
 {
@@ -1600,7 +1588,7 @@
 		 * the implicit decrement that occurs via bio_endio() in
 		 * process_prepared_discard_{passdown,no_passdown}.
 		 */
-		__bio_inc_remaining(bio);
+		atomic_inc(&bio->bi_remaining);
 		if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list))
 			pool->process_prepared_discard(m);