dt-bindings: usb: ehci: Increase the number of PHYs

"make dtbs_check":

    arch/arm/boot/dts/r8a77470-iwg23s-sbc.dtb: usb@ee080100: phys: [[17, 0], [31]] is too long
	    From schema: Documentation/devicetree/bindings/usb/generic-ehci.yaml
    arch/arm/boot/dts/r8a77470-iwg23s-sbc.dtb: usb@ee0c0100: phys: [[17, 1], [33], [21, 0]] is too long
	    From schema: Documentation/devicetree/bindings/usb/generic-ehci.yaml

Some USB EHCI controllers (e.g. on the Renesas RZ/G1C SoC) have multiple
PHYs.  Increase the maximum number of PHYs to 3, which is sufficient for
now.

Fixes: 0499220d

 ("dt-bindings: Add missing array size constraints")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/c5d19e2f9714f43effd90208798fc1936098078f.1655301043.git.geert+renesas@glider.be
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>