power_supply_sysfs: Handle -ENODATA in a special way

There are cases when some device can not report any meaningful value,
e.g. TWL4030 charger can report voltage only when charging is
active.

In these cases drivers will return -ENODATA, and we shouldn't flood
kernel log with error messages.
Signed-off-by: NAnton Vorontsov <avorontsov@ru.mvista.com>

drivers/power/power_supply_sysfs.c

@@ -65,7 +65,10 @@ static ssize_t power_supply_show_property(struct device *dev,
 	ret = psy->get_property(psy, off, &value);
 
 	if (ret < 0) {
-		if (ret != -ENODEV)
+		if (ret == -ENODATA)
+			dev_dbg(dev, "driver has no data for `%s' property\n",
+				attr->attr.name);
+		else if (ret != -ENODEV)
 			dev_err(dev, "driver failed to report `%s' property\n",
 				attr->attr.name);
 		return ret;