dt-bindings: usb: ehci: Add missing 2nd register region

The 'ibm,usb-ehci-440epx' compatible has a 2nd 'reg' region, but the
schema says there is only 1 region. Fix this.

Cc: linux-usb@vger.kernel.org
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/usb/generic-ehci.yaml

@@ -6,19 +6,30 @@ $schema: http://devicetree.org/meta-schemas/core.yaml#
 
 title: USB EHCI Controller Device Tree Bindings
 
-allOf:
-  - $ref: "usb-hcd.yaml"
-
 maintainers:
   - Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 
+allOf:
+  - $ref: "usb-hcd.yaml"
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              const: ibm,usb-ehci-440epx
+    then:
+      properties:
+        reg:
+          maxItems: 1
+
 properties:
   compatible:
     contains:
       const: generic-ehci
 
   reg:
-    maxItems: 1
+    minItems: 1
+    maxItems: 2
 
   interrupts:
     maxItems: 1