vpx_temporal_svc_encoder.sh: remove FUNCNAME bashism
vpx_temporal_svc_encoder.sh: remove FUNCNAME bashism

replace with an explicit output file prefix that matches the function
name

Change-Id: I7f6a4105adb34327b1099a5fbf132aa8d1ad5b90

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