Slight optimization of c145d19. Not supposed to result in
any visible difference.
- if UI viewport is drawn for GUI_EVENT_NEED_UI_UPDATE,
it doesn't need to do a viewport update; skin_render
already updates the display
- skin_render_deferred shouldn't need to request that
the skin perform an immediate update
Change-Id: Id03cf89357eaf0d61af1e928c94942d8c4882dba