iio:magnetometer: st_magn: add BDU settings

LIS3MDL and LSM9DS1 are missing BDU settings in their register maps, so add
them. I don't have a LIS3MDL sensor to test, but this works correctly on
the LSM9DS1, which has the same register map.

Signed-off-by: Martin Kelly <martin@martingkelly.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/magnetometer/st_magn_core.c

@@ -316,6 +316,10 @@ static const struct st_sensor_settings st_magn_sensors_settings[] = {
 				},
 			},
 		},
+		.bdu = {
+			.addr = 0x24,
+			.mask = 0x40,
+		},
 		.drdy_irq = {
 			/* drdy line is routed drdy pin */
 			.stat_drdy = {