iio: accel: adxl367: make use of iio_get_masklength()

Use iio_get_masklength() to access '.masklength' so it can be annotated
as __private when there are no more direct users of it.
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Reviewed-by: Alexandru Ardelean <aardelean@baylibre.com>
Link: https://patch.msgid.link/20240702-dev-iio-masklength-private-v1-4-98193bf536a6@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/accel/adxl367.c

@@ -1220,7 +1220,7 @@ static int adxl367_update_scan_mode(struct iio_dev *indio_dev,
 		return ret;
 
 	st->fifo_set_size = bitmap_weight(active_scan_mask,
-					  indio_dev->masklength);
+					  iio_get_masklength(indio_dev));
 
 	return 0;
 }