power: supply: sc27xx: Fix external_power_changed race

sc27xx_fgu_external_power_changed() dereferences data->battery,
which gets sets in ab8500_btemp_probe() like this:

	data->battery = devm_power_supply_register(dev, &sc27xx_fgu_desc,
                                                   &fgu_cfg);

As soon as devm_power_supply_register() has called device_add()
the external_power_changed callback can get called. So there is a window
where sc27xx_fgu_external_power_changed() may get called while
data->battery has not been set yet leading to a NULL pointer dereference.

Fixing this is easy. The external_power_changed callback gets passed
the power_supply which will eventually get stored in data->battery,
so sc27xx_fgu_external_power_changed() can simply directly use
the passed in psy argument which is always valid.

After this change sc27xx_fgu_external_power_changed() is reduced to just
"power_supply_changed(psy);" and it has the same prototype. While at it
simply replace it with making the external_power_changed callback
directly point to power_supply_changed.

Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/sc27xx_fuel_gauge.c

@@ -733,13 +733,6 @@ static int sc27xx_fgu_set_property(struct power_supply *psy,
 	return ret;
 }
 
-static void sc27xx_fgu_external_power_changed(struct power_supply *psy)
-{
-	struct sc27xx_fgu_data *data = power_supply_get_drvdata(psy);
-
-	power_supply_changed(data->battery);
-}
-
 static int sc27xx_fgu_property_is_writeable(struct power_supply *psy,
 					    enum power_supply_property psp)
 {
@@ -774,7 +767,7 @@ static const struct power_supply_desc sc27xx_fgu_desc = {
 	.num_properties		= ARRAY_SIZE(sc27xx_fgu_props),
 	.get_property		= sc27xx_fgu_get_property,
 	.set_property		= sc27xx_fgu_set_property,
-	.external_power_changed	= sc27xx_fgu_external_power_changed,
+	.external_power_changed	= power_supply_changed,
 	.property_is_writeable	= sc27xx_fgu_property_is_writeable,
 	.no_thermal		= true,
 };