z2_battery: Fix count of properties

PROP_STATUS property was not counted, as result VOLTAGE_MIN property is
missing in sysfs. Fix it.

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>