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>