dm: allow targets to return output from messages they are sent

Could be useful for a target to return stats or other information.
If a target does DMEMIT() anything to @result from its .message method
then it must return 1 to the caller.

Signed-off-By: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index a89fd8f..5acf77d 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1595,7 +1595,7 @@ static int target_message(struct file *filp, struct dm_ioctl *param, size_t para
 		DMWARN("Target message sector outside device.");
 		r = -EINVAL;
 	} else if (ti->type->message)
-		r = ti->type->message(ti, argc, argv);
+		r = ti->type->message(ti, argc, argv, result, maxlen);
 	else {
 		DMWARN("Target type does not support messages");
 		r = -EINVAL;