lguest: Point to the right directory for the lguest launcher

The code was moved in 07fe9977 but
the comment was not updated. The reference in drivers/vhost/vhost.c
is left alone as it is historic.

Signed-off-by: Holger Hans Peter Freyther <holger@moiji-mobile.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>