iio: humidity: am2315: 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-v1-8-8e12cd042906@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/humidity/am2315.c

@@ -174,8 +174,7 @@ static irqreturn_t am2315_trigger_handler(int irq, void *p)
 		data->scan.chans[1] = sensor_data.temp_data;
 	} else {
 		i = 0;
-		for_each_set_bit(bit, indio_dev->active_scan_mask,
-				 indio_dev->masklength) {
+		iio_for_each_active_channel(indio_dev, bit) {
 			data->scan.chans[i] = (bit ? sensor_data.temp_data :
 					       sensor_data.hum_data);
 			i++;