iio: adc: mcp3911: make use of the sign bit

The device supports negative values as well.

Fixes: 3a89b28 ("iio: adc: add support for mcp3911")
Signed-off-by: Marcus Folkesson <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Cameron <[email protected]>

Author: marcusfolkesson

drivers/iio/adc/mcp3911.c

@@ -113,6 +113,8 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
 		if (ret)
 			goto out;
 
+		*val = sign_extend32(*val, 23);
+
 		ret = IIO_VAL_INT;
 		break;