[Libva] Directly encoding a surface after decoding

[Timo Rothenpieler]

No, i made sure both use the same display and also validated it by 
printing it.

For me this seems like there's some code missing to initialize the bo if 
it's missing, like the VideoProcessor seems to use, but when i tried to 
add some, i just got a green video again.

>
> One of the parameters of vaCreateSurfaces() is a VA display, so a VA
> surface may only be valid to the specified VA display. Do the decoder
> and encoder use different VA displays in your app ?
>
> Thanks
> Haihao