🩹 Fix FT_MOTION_MENU lambda (#27401)

Marlin/src/lcd/menu/menu_motion.cpp

@@ -434,7 +434,7 @@ void menu_move() {
 
     bool show_state = c.active;
     EDIT_ITEM(bool, MSG_FIXED_TIME_MOTION, &show_state, []{
-      c.active ^= true;
+      ftMotion.cfg.active ^= true;
       ftMotion.update_shaping_params();
     });