iio: pressure: dlhl60d: 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/20240718-dev-iio-masklength-private2-v1-19-8e12cd042906@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/pressure/dlhl60d.c

@@ -256,8 +256,7 @@ static irqreturn_t dlh_trigger_handler(int irq, void *private)
 	if (ret)
 		goto out;
 
-	for_each_set_bit(chn, indio_dev->active_scan_mask,
-			 indio_dev->masklength) {
+	iio_for_each_active_channel(indio_dev, chn) {
 		memcpy(&tmp_buf[i++],
 			&st->rx_buf[1] + chn * DLH_NUM_DATA_BYTES,
 			DLH_NUM_DATA_BYTES);