reflog: free() ref given to us by dwim_log()

When dwim_log() returns the "ref" is always ether NULL or an
xstrdup()'d string.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/reflog.c

@@ -653,6 +653,7 @@ static int cmd_reflog_expire(int argc, const char **argv, const char *prefix)
 					should_expire_reflog_ent,
 					reflog_expiry_cleanup,
 					&cb);
+		free(ref);
 	}
 	return status;
 }