IIO: Ingenic JZ47xx: Add xlate cb to retrieve correct channel idx

Provide an of_xlate callback in order to retrieve the correct channel
specifier index from the IIO channels array.
Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
Tested-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ingenic-adc.c

@@ -401,6 +401,21 @@ static int ingenic_adc_read_raw(struct iio_dev *iio_dev,
 	}
 }
 
+static int ingenic_adc_of_xlate(struct iio_dev *iio_dev,
+				const struct of_phandle_args *iiospec)
+{
+	int i;
+
+	if (!iiospec->args_count)
+		return -EINVAL;
+
+	for (i = 0; i < iio_dev->num_channels; ++i)
+		if (iio_dev->channels[i].channel == iiospec->args[0])
+			return i;
+
+	return -EINVAL;
+}
+
 static void ingenic_adc_clk_cleanup(void *data)
 {
 	clk_unprepare(data);
@@ -410,6 +425,7 @@ static const struct iio_info ingenic_adc_info = {
 	.write_raw = ingenic_adc_write_raw,
 	.read_raw = ingenic_adc_read_raw,
 	.read_avail = ingenic_adc_read_avail,
+	.of_xlate = ingenic_adc_of_xlate,
 };
 
 static const struct iio_chan_spec ingenic_channels[] = {