Staging: iio: adis16209: Use sign_extend32 function

Use sign_extend32 function instead of manually coding
it.
Signed-off-by: Shreeya Patel <shreeya.patel23498@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/accel/adis16209.c

@@ -212,9 +212,8 @@ static int adis16209_read_raw(struct iio_dev *indio_dev,
 		ret = adis_read_reg_16(st, addr, &val16);
 		if (ret)
 			return ret;
-		val16 &= (1 << bits) - 1;
-		val16 = (s16)(val16 << (16 - bits)) >> (16 - bits);
-		*val = val16;
+
+		*val = sign_extend32(val16, bits - 1);
 		return IIO_VAL_INT;
 	}
 	return -EINVAL;