pcf50633_charger: Enable periodic charging restart

The battery charger state machine switches into charging mode when
the battery voltage falls below 96% of a battery float voltage. But
the voltage drop in Li-ion batteries is marginal(1~2 %) till about
80% of its capacity - which means, after a BATFULL, charging won't
be restarted until 80%.

This work_struct function restarts charging at regular intervals to
make sure the battery doesn't discharge too much.

Signed-off-by: Balaji Rao <balajirrao@openmoko.org>
Cc: Andy Green <andy@openmoko.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>