MAINTAINERS: add reviewers for virtio-gpu

Add Gurchetan Singh and me as reviewers for virtio-gpu.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Acked-by: Gurchetan Singh <gurchetansingh@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20211028213446.955338-1-olvaffe@gmail.com


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