regulator: da903x: Don't read/write to DA9030_INVAL/DA9034_INVAL address

For fixed voltage, DA9030_LDO13 and DA9034_LDO5, the info->vol_reg is
DA9030_INVAL/DA9034_INVAL.
It does not make sense to read/write to DA9030_INVAL/DA9034_INVAL address.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/da903x.c

@@ -107,6 +107,9 @@ static int da903x_set_voltage_sel(struct regulator_dev *rdev, unsigned selector)
 	struct device *da9034_dev = to_da903x_dev(rdev);
 	uint8_t val, mask;
 
+	if (rdev->desc->n_voltages == 1)
+		return -EINVAL;
+
 	val = selector << info->vol_shift;
 	mask = ((1 << info->vol_nbits) - 1)  << info->vol_shift;
 
@@ -120,6 +123,9 @@ static int da903x_get_voltage_sel(struct regulator_dev *rdev)
 	uint8_t val, mask;
 	int ret;
 
+	if (rdev->desc->n_voltages == 1)
+		return 0;
+
 	ret = da903x_read(da9034_dev, info->vol_reg, &val);
 	if (ret)
 		return ret;