pda_power: Fix ac_draw usage before it being set

When I reboot my iPAQ hx4700 in its cradle, the battery will not begin
to charge even though the AC supply is connected. Charging will start
only after the PDA power driver is tickled by some other power event,
such as reseating the iPAQ in its cradle or connecting the USB cable.

The problem lies in pda_power_probe(), where ac_draw is used by the call
to update_charger() before being set by the call to regulator_get().

Moving the regulator_get() call to before the update_charger() call
fixes the problem.

Signed-off-by: Paul Parsons <lost.distance@yahoo.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>