iio: adc: rockchip_saradc: Just get referenced voltage once at probe

The referenced voltage is not changed after initiation, so just only
get referenced voltage once.

Change-Id: I1eeab03f68855fafe010db328ec7bbcfa7d52310
Signed-off-by: David Wu <david.wu@rock-chips.com>

Author: SuperDavidWu

drivers/iio/adc/rockchip_saradc.c

@@ -55,6 +55,7 @@ struct rockchip_saradc {
 	struct clk		*clk;
 	struct completion	completion;
 	struct regulator	*vref;
+	int			uv_vref;
 	struct reset_control	*reset;
 	const struct rockchip_saradc_data *data;
 	u16			last_val;
@@ -65,7 +66,6 @@ static int rockchip_saradc_read_raw(struct iio_dev *indio_dev,
 				    int *val, int *val2, long mask)
 {
 	struct rockchip_saradc *info = iio_priv(indio_dev);
-	int ret;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
@@ -93,13 +93,7 @@ static int rockchip_saradc_read_raw(struct iio_dev *indio_dev,
 		mutex_unlock(&indio_dev->mlock);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
-		ret = regulator_get_voltage(info->vref);
-		if (ret < 0) {
-			dev_err(&indio_dev->dev, "failed to get voltage\n");
-			return ret;
-		}
-
-		*val = ret / 1000;
+		*val = info->uv_vref / 1000;
 		*val2 = info->data->num_bits;
 		return IIO_VAL_FRACTIONAL_LOG2;
 	default:
@@ -298,6 +292,13 @@ static int rockchip_saradc_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	info->uv_vref = regulator_get_voltage(info->vref);
+	if (info->uv_vref < 0) {
+		dev_err(&pdev->dev, "failed to get voltage\n");
+		ret = info->uv_vref;
+		goto err_reg_voltage;
+	}
+
 	ret = clk_prepare_enable(info->pclk);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to enable pclk\n");