drm/virtio: Return proper error codes instead of -1

Don't return -1 in error cases, return proper error code. The returned
error codes propagate to error messages and to userspace and it's always
good to have a meaningful error number for debugging purposes.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20220630200726.1884320-10-dmitry.osipenko@collabora.com


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>