mips: dts: ralink: mt7621: add cell count properties to usb

Add default #address-cells and #size-cells properties to the
usb node, which should be suitable for hubs and devices without
explicitly declared interface nodes, as:

   "#address-cells":
     description: should be 1 for hub nodes with device nodes,
       should be 2 for device nodes with interface nodes.
     enum: [1, 2]

   "#size-cells":
     const: 0

-- from Documentation/devicetree/bindings/usb/usb-device.yaml
Acked-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Justin Swartz <justin.swartz@risingedge.co.za>
Reviewed-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/dts/ralink/mt7621.dtsi

@@ -307,6 +307,9 @@ usb: usb@1e1c0000 {
 		       0x1e1d0700 0x0100>;
 		reg-names = "mac", "ippc";
 
+		#address-cells = <1>;
+		#size-cells = <0>;
+
 		clocks = <&sysc MT7621_CLK_XTAL>;
 		clock-names = "sys_ck";