bq27x00_battery: Call power_supply_changed only when capacity changed

In current driver, power_supply_changed() is called whenever any of
the battery attribute changed. This causes kernel to increases the
'/sys/power/wakeup_count' and make suspend not working correctly.

This patch change this behavior to call power_supply_changed()
only when the battery capacity changed.

Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>