iio: dac: ad7303: fix error return code in ad7303_probe()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/dac/ad7303.c

@@ -235,8 +235,10 @@ static int ad7303_probe(struct spi_device *spi)
 
 	if (ext_ref) {
 		st->vref_reg = regulator_get(&spi->dev, "REF");
-		if (IS_ERR(st->vref_reg))
+		if (IS_ERR(st->vref_reg)) {
+			ret = PTR_ERR(st->vref_reg);
 			goto err_disable_vdd_reg;
+		}
 
 		ret = regulator_enable(st->vref_reg);
 		if (ret)