So far we simply ignored it for MEMORY_DMABUF passthrough caps without known negative cosequences, but with upcoming more complicated caps negotiations it's becoming an issue, thus fix it. Fixes: 7e71d4f753 ("gl: upload: Add DMA_DRM passthrough upload") Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8964>