logind: use gcc empty structure initialization

src/login/logind-session.c

@@ -1181,7 +1181,7 @@ static int session_open_vt(Session *s) {
 
 int session_prepare_vt(Session *s) {
         int vt, r;
-        struct vt_mode mode = { 0 };
+        struct vt_mode mode = {};
 
         if (s->vtnr < 1)
                 return 0;