We have only one copy of gst_va_base_dec_parent_class inside the
vabasedec, so it can not handle the case when there are multi va
decoders inside one pipeline. The pipeline:
gst-launch-1.0 filesrc location=xxx.h264 ! h264parse \
! vah264dec ! msdkh265enc ! vah265dec ! fakesink
generates a assertion of
"invalid cast from 'GstVaH264Dec' to 'GstH265Decoder"
and gets a crash.
We should keep the parent_class for each decoder type.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2231>
64b596103a