power: supply: axp288_fuel_gauge: Fix external_power_changed race

fuel_gauge_external_power_changed() dereferences info->bat,
which gets sets in axp288_fuel_gauge_probe() like this:

  info->bat = devm_power_supply_register(dev, &fuel_gauge_desc, &psy_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 fuel_gauge_external_power_changed() may get called while
info->bat 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 info->bat,
so fuel_gauge_external_power_changed() can simply directly use
the passed in psy argument which is always valid.

Fixes: 30abb3d ("power: supply: axp288_fuel_gauge: Take lock before updating the valid flag")
Cc: stable@vger.kernel.org
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/axp288_fuel_gauge.c

@@ -507,7 +507,7 @@ static void fuel_gauge_external_power_changed(struct power_supply *psy)
 	mutex_lock(&info->lock);
 	info->valid = 0; /* Force updating of the cached registers */
 	mutex_unlock(&info->lock);
-	power_supply_changed(info->bat);
+	power_supply_changed(psy);
 }
 
 static struct power_supply_desc fuel_gauge_desc = {