vp9: On change_config() only call update_frame_size if needed.
vp9: On change_config() only call update_frame_size if needed.

change_config() may be called often in real-time application,
to update bitrate/framerate or qp-max/min.
No need to do update_frame_size() unless frame size has changed.

Change-Id: I23a51deade1e03adc91c468f9ffde3235298770c

mwgoldsmith/vpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,mwgoldsmith/vpx,Topopiccione/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/vpx,Topopiccione/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,Topopiccione/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx