dt-bindings: soc: rockchip: drop unnecessary #phy-cells from grf.yaml

The recent yaml conversion of the grf and inno-usb2-phy bindings
left the #phy-cells in place in the main usb2phy node inside the
example in grf.yaml, causing new warnings.

Drop it to make the bindingcheck happy.

Fixes: e71ccdff37 ("dt-bindings: phy: rename phy nodename in phy-rockchip-inno-usb2.yaml")
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210607141845.3331910-1-heiko@sntech.de

Documentation/devicetree/bindings/soc/rockchip/grf.yaml

@@ -242,7 +242,6 @@ examples:
         clock-names = "phyclk";
         #clock-cells = <0>;
         clock-output-names = "clk_usbphy0_480m";
-        #phy-cells = <0>;
 
         u2phy0_host: host-port {
           #phy-cells = <0>;