staging:iio:accel:adis16203: sign extend function rather code duplication

Use sign_extend32 kernel function instead of code duplication.
This function is also safe for 16 bits.
Signed-off-by: Karim Eshapa <karim.eshapa@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/accel/adis16203.c

@@ -168,7 +168,6 @@ static int adis16203_read_raw(struct iio_dev *indio_dev,
 {
 	struct adis *st = iio_priv(indio_dev);
 	int ret;
-	int bits;
 	u8 addr;
 	s16 val16;
 
@@ -202,14 +201,11 @@ static int adis16203_read_raw(struct iio_dev *indio_dev,
 		*val = 25000 / -470 - 1278; /* 25 C = 1278 */
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_CALIBBIAS:
-		bits = 14;
 		addr = adis16203_addresses[chan->scan_index];
 		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, 13);
 		return IIO_VAL_INT;
 	default:
 		return -EINVAL;