wayland/dma-buf: Handle failing to import scanout DMA buffer
A DMA buffer might not be able to scanout, and in that case the import with GBM_BO_USE_SCANOUT will fail. Handle that by failing to scanout, effectively falling back to compositing.
I don't have a driver combination where this happens, but in theory it could.
Edited by Georges Basile Stavracas Neto