libusb: do not depend on host-udev for host variant

Commit 25926af5 disabled udev support for the host variant, but forgot to
remove it from the (implicit) host dependencies.

Also reordered things to keep the HOST_* definitions together.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>