iio: adc: ad7266: Don't set error code to st->vref_uv

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/adc/ad7266.c

@@ -411,7 +411,11 @@ static int __devinit ad7266_probe(struct spi_device *spi)
 		if (ret)
 			goto error_put_reg;
 
-		st->vref_uv = regulator_get_voltage(st->reg);
+		ret = regulator_get_voltage(st->reg);
+		if (ret < 0)
+			goto error_disable_reg;
+
+		st->vref_uv = ret;
 	} else {
 		/* Use internal reference */
 		st->vref_uv = 2500000;