networkd: link - fix reading routes

This regressed during the port to extract_first_word in c598ac76
(v228).

CID #1338083

src/network/networkd-link.c

@@ -2327,6 +2327,8 @@ network_file_fail:
         }
 
         if (routes) {
+                p = routes;
+
                 for (;;) {
                         Route *route;
                         _cleanup_free_ char *route_str = NULL;