dt-bindings: net: mvusb: Fix example errors

The example for Marvell USB to MDIO Controller doesn't build:

Error: Documentation/devicetree/bindings/net/marvell,mvusb.example.dts:18.9-14 syntax error
FATAL ERROR: Unable to parse input tree

This is due to label refs being used which can't be resolved.

Fixes: 61e0150c ("dt-bindings: net: add marvell usb to mdio bindings")
Cc: Tobias Waldekranz <tobias@waldekranz.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/marvell,mvusb.yaml

@@ -38,20 +38,18 @@ required:
 examples:
   - |
     /* USB host controller */
-    &usb1 {
-            mvusb: mdio@1 {
+    usb {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            mdio@1 {
                     compatible = "usb1286,1fa4";
                     reg = <1>;
                     #address-cells = <1>;
                     #size-cells = <0>;
-            };
-    };
 
-    /* MV88E6390X devboard */
-    &mvusb {
                     switch@0 {
                             compatible = "marvell,mv88e6190";
-                    status = "ok";
                             reg = <0x0>;
 
                             ports {
@@ -63,3 +61,4 @@ examples:
                             };
                     };
             };
+    };