iio: proximity: sx_common: 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-v1-22-8e12cd042906@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/proximity/sx_common.c

@@ -369,8 +369,7 @@ static irqreturn_t sx_common_trigger_handler(int irq, void *private)
 
 	mutex_lock(&data->mutex);
 
-	for_each_set_bit(bit, indio_dev->active_scan_mask,
-			 indio_dev->masklength) {
+	iio_for_each_active_channel(indio_dev, bit) {
 		ret = data->chip_info->ops.read_prox_data(data,
 						     &indio_dev->channels[bit],
 						     &val);
@@ -398,8 +397,7 @@ static int sx_common_buffer_preenable(struct iio_dev *indio_dev)
 	int bit, ret;
 
 	mutex_lock(&data->mutex);
-	for_each_set_bit(bit, indio_dev->active_scan_mask,
-			 indio_dev->masklength)
+	iio_for_each_active_channel(indio_dev, bit)
 		__set_bit(indio_dev->channels[bit].channel, &channels);
 
 	ret = sx_common_update_chan_en(data, channels, data->chan_event);