drm/virtio: clean up minor codestyle issues

Fix codestyle warnings and errors generated by CHECKPATCH in virtio
source files.

Signed-off-by: Athul Raj Kollareth <krathul3152@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://lore.kernel.org/r/20250813062109.5326-1-krathul3152@gmail.com