iio: ti-adc12138: Use scan_type when processing raw data

Use channel definition as root of trust and replace constant
when reading elements directly using the raw sysfs attributes.
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Link: https://lore.kernel.org/r/20211104082413.3681212-10-gwendal@chromium.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ti-adc12138.c

@@ -239,7 +239,8 @@ static int adc12138_read_raw(struct iio_dev *iio,
 		if (ret)
 			return ret;
 
-		*value = sign_extend32(be16_to_cpu(data) >> 3, 12);
+		*value = sign_extend32(be16_to_cpu(data) >> channel->scan_type.shift,
+				       channel->scan_type.realbits - 1);
 
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE: