iio: accel: adxl380: 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>
Link: https://patch.msgid.link/20240726-dev-iio-masklength-private3-v1-1-82913fc0fb87@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/accel/adxl380.c

@@ -1110,7 +1110,7 @@ static int adxl380_buffer_postenable(struct iio_dev *indio_dev)
 	}
 
 	st->fifo_set_size = bitmap_weight(indio_dev->active_scan_mask,
-					  indio_dev->masklength);
+					  iio_get_masklength(indio_dev));
 
 	if ((st->watermark * st->fifo_set_size) > ADXL380_FIFO_SAMPLES)
 		st->watermark = (ADXL380_FIFO_SAMPLES  / st->fifo_set_size);