Fix bugs found through compiler warnings

src/drivers/mkblctrl/mkblctrl.cpp

@@ -131,8 +131,8 @@ public:
 	int		set_motor_count(unsigned count);
 	int		set_motor_test(bool motortest);
 	int		set_overrideSecurityChecks(bool overrideSecurityChecks);
-	int		set_px4mode(int px4mode);
-	int		set_frametype(int frametype);
+	void	set_px4mode(int px4mode);
+	void	set_frametype(int frametype);
 	unsigned int		mk_check_for_blctrl(unsigned int count, bool showOutput, bool initI2C);
 
 private:
@@ -330,13 +330,13 @@ MK::set_update_rate(unsigned rate)
 	return OK;
 }
 
-int
+void
 MK::set_px4mode(int px4mode)
 {
 	_px4mode = px4mode;
 }
 
-int
+void
 MK::set_frametype(int frametype)
 {
 	_frametype = frametype;

src/drivers/px4fmu/fmu.cpp

@@ -741,7 +741,7 @@ PX4FMU::task_main()
 	}
 
 	for (unsigned i = 0; i < NUM_ACTUATOR_CONTROL_GROUPS; i++) {
-		if (_control_subs > 0) {
+		if (_control_subs[i] > 0) {
 			::close(_control_subs[i]);
 			_control_subs[i] = -1;
 		}

src/drivers/roboclaw/RoboClaw.cpp

@@ -182,7 +182,10 @@ float RoboClaw::getMotorPosition(e_motor motor)
 		return _motor1Position;
 	} else if (motor == MOTOR_2) {
 		return _motor2Position;
-	}
+	} else {
+        warnx("Unknown motor value passed to RoboClaw::getMotorPosition");
+        return NAN;
+    }
 }
 
 float RoboClaw::getMotorSpeed(e_motor motor)
@@ -191,7 +194,10 @@ float RoboClaw::getMotorSpeed(e_motor motor)
 		return _motor1Speed;
 	} else if (motor == MOTOR_2) {
 		return _motor2Speed;
-	}
+	} else {
+        warnx("Unknown motor value passed to RoboClaw::getMotorPosition");
+        return NAN;
+    }
 }
 
 int RoboClaw::setMotorSpeed(e_motor motor, float value)