iio: imu: bmi160_core: 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-v1-9-8e12cd042906@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/bmi160/bmi160_core.c

@@ -435,8 +435,7 @@ static irqreturn_t bmi160_trigger_handler(int irq, void *p)
 	int i, ret, j = 0, base = BMI160_REG_DATA_MAGN_XOUT_L;
 	__le16 sample;
 
-	for_each_set_bit(i, indio_dev->active_scan_mask,
-			 indio_dev->masklength) {
+	iio_for_each_active_channel(indio_dev, i) {
 		ret = regmap_bulk_read(data->regmap, base + i * sizeof(sample),
 				       &sample, sizeof(sample));
 		if (ret)