drm/virtio: drop virtio_gpu_execbuffer_ioctl() wrapping

Instead of wrapping virtio_gpu_execbuffer() to execute the ioctl
just execute it directly.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Message-id: 1472660813-28219-1-git-send-email-gustavo@padovan.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>