iio: adc: ti-ads1298: make use of iio_for_each_active_channel()

Use iio_for_each_active_channel() to iterate over active channels
accessing '.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-v1-14-82913fc0fb87@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ti-ads1298.c

@@ -502,8 +502,7 @@ static void ads1298_rdata_complete(void *context)
 	}
 
 	/* Demux the channel data into our bounce buffer */
-	for_each_set_bit(scan_index, indio_dev->active_scan_mask,
-			 indio_dev->masklength) {
+	iio_for_each_active_channel(indio_dev, scan_index) {
 		const struct iio_chan_spec *scan_chan =
 					&indio_dev->channels[scan_index];
 		const u8 *data = priv->rx_buffer + scan_chan->address;