dm: clear bi_end_io on remapping failure

As a precaution, set bi_end_io to NULL when failing to remap.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b89c548..e24143c 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1016,6 +1016,7 @@
 		/*
 		 * Store bio_set for cleanup.
 		 */
+		clone->bi_end_io = NULL;
 		clone->bi_private = md->bs;
 		bio_put(clone);
 		free_tio(md, tio);