virtio_9p.h needs <linux/types.h>

Found with makes headers_check:
include/linux/virtio_9p.h:15: found __[us]{8,16,32,64} type without #include <linux/types.h>

Signed-off-by: Fang Wenqi <antonf@turbolinux.com.cn>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>