iio: dac: ad5380: Don't set error code to st->vref

regulator_get_voltage() may return negative error code.
Add error checking to avoid setting error code to st->vref_uv.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/dac/ad5380.c

@@ -406,7 +406,11 @@ static int __devinit ad5380_probe(struct device *dev, struct regmap *regmap,
 			goto error_free_reg;
 		}
 
-		st->vref = regulator_get_voltage(st->vref_reg);
+		ret = regulator_get_voltage(st->vref_reg);
+		if (ret < 0)
+			goto error_disable_reg;
+
+		st->vref = ret;
 	} else {
 		st->vref = st->chip_info->int_vref;
 		ctrl |= AD5380_CTRL_INT_VREF_EN;