Add missing code in merge commit e890e6e8d8bd
("v4l2: Fix use after free of fmtdesc"). The v4l2object code was
missing.
Related to https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4317
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4411>