regulator: core: Report microvolts in sysfs even with only list_voltage()

If a regulator only supports a single voltage list_voltage() can be used
to report what that voltage is so add this as one of the criteria for
creating the microvolts file in sysfs.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/core.c

@@ -3020,7 +3020,8 @@ static int add_regulator_attributes(struct regulator_dev *rdev)
 
 	/* some attributes need specific methods to be displayed */
 	if ((ops->get_voltage && ops->get_voltage(rdev) >= 0) ||
-	    (ops->get_voltage_sel && ops->get_voltage_sel(rdev) >= 0)) {
+	    (ops->get_voltage_sel && ops->get_voltage_sel(rdev) >= 0) ||
+	    (ops->list_voltage && ops->list_voltage(rdev, 0) >= 0)) {
 		status = device_create_file(dev, &dev_attr_microvolts);
 		if (status < 0)
 			return status;