vp9: SVC: Fix setting in sample encoder.
vp9: SVC: Fix setting in sample encoder.

For 1 spatial layer case, scaling_num/den was not set properly.

Change-Id: I139bf70c6dffde89eed24e435bcb5d98d2029bcd

ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx