px4_main_t: fix method declaration throughout the code base

px4_main_t is defined as:
typedef int (*px4_main_t)(int argc, char *argv[]);
which matches with the definition in NuttX, given to task_create

src/modules/events/temperature_calibration/task.cpp

@@ -83,7 +83,7 @@ public:
 	 */
 	int		start();
 
-	static void do_temperature_calibration(int argc, char *argv[]);
+	static int do_temperature_calibration(int argc, char *argv[]);
 
 	void		task_main();
 
@@ -320,9 +320,10 @@ void TemperatureCalibration::task_main()
 	PX4_INFO("Exiting temperature calibration task");
 }
 
-void TemperatureCalibration::do_temperature_calibration(int argc, char *argv[])
+int TemperatureCalibration::do_temperature_calibration(int argc, char *argv[])
 {
 	temperature_calibration::instance->task_main();
+	return 0;
 }
 
 int TemperatureCalibration::start()