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/gnd_att_control/GroundRoverAttitudeControl.cpp

@@ -174,10 +174,11 @@ GroundRoverAttitudeControl::battery_status_poll()
 	}
 }
 
-void
+int
 GroundRoverAttitudeControl::task_main_trampoline(int argc, char *argv[])
 {
 	att_gnd_control::g_control->task_main();
+	return 0;
 }
 
 void

src/modules/gnd_att_control/GroundRoverAttitudeControl.hpp

@@ -136,7 +136,7 @@ private:
 	void		vehicle_attitude_setpoint_poll();
 	void		battery_status_poll();
 
-	static void	task_main_trampoline(int argc, char *argv[]);
+	static int	task_main_trampoline(int argc, char *argv[]);
 	void		task_main();
 
 };