builtin-reflog.c: fix typo that accesses an unset variable

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin-reflog.c b/builtin-reflog.c
index f422693..5e54989 100644
--- a/builtin-reflog.c
+++ b/builtin-reflog.c
@@ -394,7 +394,7 @@
 		int recno;
 
 		if (!spec) {
-			status |= error("Not a reflog: %s", ref);
+			status |= error("Not a reflog: %s", argv[i]);
 			continue;
 		}