ACPI / AC: recheck adapter status upon battery status changes

On HP Pavilion dv6-6179er there are no notifications when AC adapter
is plugged/unplugged.
However, when AC status is read (acpi_ac_get_state), and if AC status
has changed, AML code triggers the notification.

This patch solves the problem by re-reading AC adapter status upon
ACPI_BATTERY_NOTIFY_STATUS notification.

Signed-off-by: Alexander Mezin <mezin.alexander@gmail.com>
Acked-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>