Rover: correct compilation when logging is disabled

APMrover2/APMrover2.cpp

@@ -82,7 +82,9 @@ const AP_Scheduler::Task Rover::scheduler_tasks[] = {
     SCHED_TASK(one_second_loop,         1,   1500),
     SCHED_TASK(compass_cal_update,     50,    200),
     SCHED_TASK(accel_cal_update,       10,    200),
+#if LOGGING_ENABLED == ENABLED
     SCHED_TASK_CLASS(DataFlash_Class,     &rover.DataFlash,        periodic_tasks, 50,  300),
+#endif
     SCHED_TASK_CLASS(AP_InertialSensor,   &rover.ins,              periodic,       50,  200),
     SCHED_TASK_CLASS(AP_Scheduler,        &rover.scheduler,        update_logging, 0.1, 200),
     SCHED_TASK_CLASS(AP_Button,           &rover.button,           update,          5,  200),

APMrover2/Log.cpp

@@ -345,5 +345,6 @@ void Rover::Log_Write_Error(uint8_t sub_system, uint8_t error_code) {}
 void Rover::Log_Write_Steering() {}
 void Rover::Log_Write_WheelEncoder() {}
 void Rover::Log_Write_Proximity() {}
+void Rover::Log_Write_Vehicle_Startup_Messages() {}
 
 #endif  // LOGGING_ENABLED

APMrover2/system.cpp

@@ -189,10 +189,12 @@ void Rover::startup_ground(void)
     mission.init();
 
     // initialise DataFlash library
+#if LOGGING_ENABLED == ENABLED
     DataFlash.set_mission(&mission);
     DataFlash.setVehicle_Startup_Log_Writer(
         FUNCTOR_BIND(&rover, &Rover::Log_Write_Vehicle_Startup_Messages, void)
         );
+#endif
 
     // we don't want writes to the serial port to cause us to pause
     // so set serial ports non-blocking once we are ready to drive