On Asus GL502VSK and UX305LA, ACPI incorrectly reports discharging when
battery is full and AC is plugged.

However rate_now is correct under this circumstance, hence we can use
"rate_now == 0" as a predicate to report battery full status correctly.

Link: https://bugs.launchpad.net/bugs/1482390Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>