MAINTAINERS: Add Dmitry Osipenko as drm/virtio co-maintainer

MAINTAINERS: Add Dmitry Osipenko as drm/virtio co-maintainer

I was helping to co-maintain VirtIO-GPU driver in drm-misc with
permission from Gerd Hoffmann for past 2 years and would like to
receive new patches directly into my inbox. Add myself as co-maintainer.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: https://lore.kernel.org/r/20250401130151.2238772-1-dmitry.osipenko@collabora.com