camera_capture: refactor to simplify capture channel initialization

src/drivers/camera_capture/camera_capture.cpp

@@ -71,9 +71,6 @@ CameraCapture::CameraCapture() :
 	_p_camera_capture_edge = param_find("CAM_CAP_EDGE");
 	param_get(_p_camera_capture_edge, &_camera_capture_edge);
 
-	// get the capture channel from function configuration params
-	_capture_channel = -1;
-
 	for (unsigned i = 0; i < 16 && _capture_channel == -1; ++i) {
 		char param_name[17];
 		snprintf(param_name, sizeof(param_name), "%s_%s%d", PARAM_PREFIX, "FUNC", i + 1);

src/drivers/camera_capture/camera_capture.hpp

@@ -96,7 +96,7 @@ public:
 	static struct work_s	_work_publisher;
 
 private:
-	int _capture_channel = 5; ///< by default, use FMU output 6
+	int _capture_channel{-1};
 
 	// Publishers
 	uORB::Publication<vehicle_command_ack_s>	_command_ack_pub{ORB_ID(vehicle_command_ack)};