Now that VideoPool accept DMA DRM, it is quite likely that the size does not get
provided in the configuration even if the format have a matching GstVideoFormat.
Fix this by reporting back the minimum expected size in the configuration. This
allows the configuration handshake to succeed.
Fixes regression caused by !9345
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9600>