dt-bindings: usb: ti,hd3ss3220: Update interrupt property as optional

On some platforms(for eg: RZ/V2M EVK), interrupt is not populated. Update
the binding to make interrupt property as optional.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20221209171836.71610-2-biju.das.jz@bp.renesas.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>