On gauges where the current register is signed, there is no charging
flag in the flags register. So only checking flags will not result
in power_supply_changed() getting called when e.g. a charger is plugged
in and the current sign changes from negative (discharging) to
positive (charging).

This causes userspace's notion of the status to lag until userspace
does a poll.

And when a power_supply_leds.c LED trigger is used to indicate charging
status with a LED, this LED will lag until the capacity percentage
changes, which may take many minutes (because the LED trigger only is
updated on power_supply_changed() calls).

Fix this by calling bq27xxx_battery_current_and_status() on gauges with
a signed current register and checking if the status has changed.

Fixes: 297a533b ("bq27x00: Cache battery registers")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>