sensors (accel/gyro/mag) determine if external with device id

src/drivers/magnetometer/hmc5883/HMC5883.cpp

@@ -48,7 +48,6 @@ HMC5883::HMC5883(device::Device *interface, const I2CSPIDriverConfig &config) :
 	_temperature_counter(0),
 	_temperature_error_count(0)
 {
-	_px4_mag.set_external(_interface->external());
 }
 
 HMC5883::~HMC5883()
@@ -367,7 +366,7 @@ int HMC5883::collect()
 	 * to align the sensor axes with the board, x and y need to be flipped
 	 * and y needs to be negated
 	 */
-	if (!_px4_mag.external()) {
+	if (!_interface->external()) {
 		// convert onboard so it matches offboard for the
 		// scaling below
 		report.y = -report.y;