vaapidecode: do not discard video info props when the format changed.
vaapidecode: do not discard video info props when the format changed.

gst_video_info_set_format() does not preserve video info properties. In
order to keep important information in the caps such as interlace mode,
framerate, pixel aspect ratio, ... we need to manually copy back those
properties after setting the new video format.

https://bugzilla.gnome.org/show_bug.cgi?id=722276

CapOM/gstreamer-vaapi,CapOM/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,CapOM/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi