vaapidecode: intersect with filter in getcaps()
vaapidecode: intersect with filter in getcaps()

In commit 6034734d I forgot to add the caps filter intersection in the
getcaps() vmethod generating a regression when a capsfilter is set in the
pipeline.

This commit adds the caps filter intersection.

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