staging:iio:adxrs450: Perform sign extension for the calibbias register

The calibbias (DNC) register contains a 10-bit twos complement value. Perform a
proper sign extension when reading the register, otherwise negative will
incorrectly be displayed as large positive values.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/gyro/adxrs450_core.c

@@ -326,7 +326,7 @@ static int adxrs450_read_raw(struct iio_dev *indio_dev,
 		ret = adxrs450_spi_read_reg_16(indio_dev, ADXRS450_DNC1, &t);
 		if (ret)
 			break;
-		*val = t;
+		*val = sign_extend32(t, 9);
 		ret = IIO_VAL_INT;
 		break;
 	default: