Fix minor issues on hildon-pannable-area.c

Fix minor issues on hildon-pannable-area.c

* src/hildon-pannable-area.c
(hildon_pannable_area_init): set scroll_delay_counter and scrollbar_fade_delay
to 0
(hildon_pannable_area_initial_effect): avoid to compute horizontal and
vertical scrollbar visibility, and use the data on private section instead,
remove the initial_hint check
(hildon_pannable_area_expose_event): add the initial_hint check here