iio: accel: kxsd9: fix the usage of spi_w8r8()

These two spi_w8r8() calls return a value with is used by the code
following the error check. The dubious use was caused by a cleanup
patch.

Fixes: d34dbee8 ("staging:iio:accel:kxsd9 cleanup and conversion to iio_chan_spec.")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/accel/kxsd9.c

@@ -81,7 +81,7 @@ static int kxsd9_write_scale(struct iio_dev *indio_dev, int micro)
 
 	mutex_lock(&st->buf_lock);
 	ret = spi_w8r8(st->us, KXSD9_READ(KXSD9_REG_CTRL_C));
-	if (ret)
+	if (ret < 0)
 		goto error_ret;
 	st->tx[0] = KXSD9_WRITE(KXSD9_REG_CTRL_C);
 	st->tx[1] = (ret & ~KXSD9_FS_MASK) | i;
@@ -163,7 +163,7 @@ static int kxsd9_read_raw(struct iio_dev *indio_dev,
 		break;
 	case IIO_CHAN_INFO_SCALE:
 		ret = spi_w8r8(st->us, KXSD9_READ(KXSD9_REG_CTRL_C));
-		if (ret)
+		if (ret < 0)
 			goto error_ret;
 		*val2 = kxsd9_micro_scales[ret & KXSD9_FS_MASK];
 		ret = IIO_VAL_INT_PLUS_MICRO;