ab8500-chargalg: Update battery health on safety timer exp

When the charging safety timer elapses, the battery health is
shown as "Good". This is misleading and also makes it difficult
to distinguish issues relating to discharging despite the fact
that the charger is still connected.

When in actual fact a safety timer elapse is an indication of a
fault in the battery. Here we make this clearer by reporting
POWER_SUPPLY_HEALTH_UNSPEC_FAILURE instead.

Signed-off-by: Lee Jones <lee.jones@linaro.org>