arm64: dts: renesas: r8a77965: Add #phy-cells property

Add "#phy-cells" property to "usb-phy@e65ee000" device node.

This silences the following DTC compiler warning:
Warning (phys_property): Missing property '#phy-cells' in node
/soc/usb-phy@e65ee000 or bad phandle (referred from
/soc/usb@ee020000:phys[0])

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>