tools/virtio: include asm/bug.h

WARN_ON is used in drivers/vhost/vringh.c, to avoid build failure,
need include asm/bug.h

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20201209084205.24062-2-peng.fan@oss.nxp.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>