decoder: h264: clean-ups.
decoder: h264: clean-ups.

Fix GST_VAAPI_PICTURE_IS_{INTER_VIEW,ANCHOR}() definitions to use
the base GST_VAAPI_PICTURE_FLAG_IS_SET() macro.

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