libvlc: set the decoder device to use with external D3D rendering

This ensures the external device is used by the D3D modules as the callbacks to
get it moved in the decoder device (rather than the display module). This allows
decoding with the device of the host and rendering with a compatible device as well.

lib/media_player.c

@@ -1088,11 +1088,13 @@ bool libvlc_video_direct3d_set_callbacks(libvlc_media_player_t *mp,
     {
         var_SetString ( mp, "vout", "direct3d11" );
         var_SetString ( mp, "avcodec-hw", "d3d11va");
+        var_SetString ( mp, "dec-dev", "d3d11-device" );
     }
     else if ( engine == libvlc_video_direct3d_engine_d3d9 )
     {
         var_SetString ( mp, "vout", "direct3d9" );
         var_SetString ( mp, "avcodec-hw", "dxva2");
+        var_SetString ( mp, "dec-dev", "d3d9-device" );
     }
     else
         return false;