dt-bindings: phy-lpc18xx-usb-otg: remove unit address from binding

DT bindings should either use a unit address and a reg property
or none of them. Since either of them aren't really useful for
such a simple device like this one remove the unit address.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>