staging:iio:accel:adis16240: sign extend function replace hard code duplication

Use sign_extend32 kernel function instead of code duplication,
Safe also for 16 bit. and remove declaration of bits variable not needed.
Signed-off-by: Karim Eshapa <karim.eshapa@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/accel/adis16240.c

@@ -250,7 +250,6 @@ static int adis16240_read_raw(struct iio_dev *indio_dev,
 {
 	struct adis *st = iio_priv(indio_dev);
 	int ret;
-	int bits;
 	u8 addr;
 	s16 val16;
 
@@ -287,24 +286,18 @@ static int adis16240_read_raw(struct iio_dev *indio_dev,
 		*val = 25000 / 244 - 0x133; /* 25 C = 0x133 */
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_CALIBBIAS:
-		bits = 10;
 		addr = adis16240_addresses[chan->scan_index][0];
 		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, 9);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_PEAK:
-		bits = 10;
 		addr = adis16240_addresses[chan->scan_index][1];
 		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, 9);
 		return IIO_VAL_INT;
 	}
 	return -EINVAL;