staging: iio: impedance-analyzer: ad5933: 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-v1-22-82913fc0fb87@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/impedance-analyzer/ad5933.c

@@ -547,7 +547,8 @@ static int ad5933_ring_preenable(struct iio_dev *indio_dev)
 	struct ad5933_state *st = iio_priv(indio_dev);
 	int ret;
 
-	if (bitmap_empty(indio_dev->active_scan_mask, indio_dev->masklength))
+	if (bitmap_empty(indio_dev->active_scan_mask,
+			 iio_get_masklength(indio_dev)))
 		return -EINVAL;
 
 	ret = ad5933_reset(st);
@@ -625,7 +626,7 @@ static void ad5933_work(struct work_struct *work)
 
 	if (status & AD5933_STAT_DATA_VALID) {
 		int scan_count = bitmap_weight(indio_dev->active_scan_mask,
-					       indio_dev->masklength);
+					       iio_get_masklength(indio_dev));
 		ret = ad5933_i2c_read(st->client,
 				test_bit(1, indio_dev->active_scan_mask) ?
 				AD5933_REG_REAL_DATA : AD5933_REG_IMAG_DATA,