iio: ad7266: 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/20211104082413.3681212-8-gwendal@chromium.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7266.c

@@ -159,7 +159,8 @@ static int ad7266_read_raw(struct iio_dev *indio_dev,
 
 		*val = (*val >> 2) & 0xfff;
 		if (chan->scan_type.sign == 's')
-			*val = sign_extend32(*val, 11);
+			*val = sign_extend32(*val,
+					     chan->scan_type.realbits - 1);
 
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE: