iio: light: tcs3472: 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-v1-17-8e12cd042906@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/tcs3472.c

@@ -383,8 +383,7 @@ static irqreturn_t tcs3472_trigger_handler(int irq, void *p)
 	if (ret < 0)
 		goto done;
 
-	for_each_set_bit(i, indio_dev->active_scan_mask,
-		indio_dev->masklength) {
+	iio_for_each_active_channel(indio_dev, i) {
 		ret = i2c_smbus_read_word_data(data->client,
 			TCS3472_CDATA + 2*i);
 		if (ret < 0)