It was never correct to not clear them.  Due to commit "3912e66a
virtio-vga: fix reset." this became more obvious though.  The virtio
rings get properly reset now, and trying to process the stale commands
will trigger an assert in the virtio core.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20190314115358.26678-3-kraxel@redhat.com