staging:iio:adis16080: Perform sign extension

The adis16080 reports sample values in twos complement. So we need to perform a
sign extension on the result, otherwise negative values will be reported
incorrectly as large positive values.
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/staging/iio/gyro/adis16080_core.c

@@ -69,7 +69,7 @@ static int adis16080_spi_read(struct iio_dev *indio_dev,
 	ret = spi_read(st->us, st->buf, 2);
 
 	if (ret == 0)
-		*val = ((st->buf[0] & 0xF) << 8) | st->buf[1];
+		*val = sign_extend32(((st->buf[0] & 0xF) << 8) | st->buf[1], 11);
 	mutex_unlock(&st->buf_lock);
 
 	return ret;