Plane: Adjust for new AP_Scheduler syntax

ArduPlane/ArduPlane.pde

@@ -824,7 +824,7 @@ void setup() {
     init_ardupilot();
 
     // initialise the main loop scheduler
-    scheduler.init(&scheduler_tasks[0], sizeof(scheduler_tasks)/sizeof(scheduler_tasks[0]));
+    scheduler.init(&scheduler_tasks[0], sizeof(scheduler_tasks)/sizeof(scheduler_tasks[0]), NULL);
 }
 
 void loop()