volume_id: abort early on read failures.
 should help with probing missing fdd's

diff --git a/util-linux/volume_id/luks.c b/util-linux/volume_id/luks.c
index b0f0f5b..ebc7d16 100644
--- a/util-linux/volume_id/luks.c
+++ b/util-linux/volume_id/luks.c
@@ -80,8 +80,9 @@
 		1 : -1];
 };
 
-int volume_id_probe_luks(struct volume_id *id, uint64_t off)
+int volume_id_probe_luks(struct volume_id *id /*,uint64_t off*/)
 {
+#define off ((uint64_t)0)
 	struct luks_phdr *header;
 
 	header = volume_id_get_buffer(id, off, sizeof(*header));