dm: add argument identifier names

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index 570a772..170eac3 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -95,7 +95,7 @@ struct core_exception {
 };
 
 struct commit_callback {
-	void (*callback)(void *, int success);
+	void (*callback)(void *ref, int success);
 	void *context;
 };