print error only if the mavlink command fails

In some cases we printed also the mavlink commands that replied
to be unsupported. This is not an error to show in the log.

src/modules/mavlink/mavlink_receiver.cpp

@@ -780,7 +780,7 @@ MavlinkReceiver::handle_message_command_ack(mavlink_message_t *msg)
 	_cmd_ack_pub.publish(command_ack);
 
 	// TODO: move it to the same place that sent the command
-	if (ack.result != MAV_RESULT_ACCEPTED && ack.result != MAV_RESULT_IN_PROGRESS) {
+	if (ack.result == MAV_RESULT_FAILED) {
 		if (msg->compid == MAV_COMP_ID_CAMERA) {
 			PX4_WARN("Got unsuccessful result %" PRIu8 " from camera", ack.result);
 		}