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: Anton Vorontsov <avorontsov@ru.mvista.com>
diff --git a/drivers/power/power_supply_sysfs.c b/drivers/power/power_supply_sysfs.c
index 0814439..c790e0c 100644
--- a/drivers/power/power_supply_sysfs.c
+++ b/drivers/power/power_supply_sysfs.c
@@ -65,7 +65,10 @@
 	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;