When a device is derived from a source device, there are at least 2
devices, and usually the derived device is the expected device, so let's
pick the last device if user doesn't specify the filter device with
filter_hw_device option

After applying this patch, the command below can work:

$> ffmpeg -init_hw_device vaapi=va:/dev/dri/renderD128 -init_hw_device
qsv=hw@va -f lavfi -i yuvtestsrc  -vf
format=nv12,hwupload=extra_hw_frames=64 -c:v h264_qsv -y out.h264
Reviewed-by: Soft Works <softworkz@hotmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>