doc: dt-binding: cdns,usb3: Add interrupt-names property under required

In the driver the interrupts are fetched by name. Therefore, add
interrupt names in the list of required properties

Fixes: 68989fe1c3 ("dt-bindings: usb: Convert cdns-usb3.txt to YAML schema")
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20210528060657.29100-1-a-govindraju@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/cdns,usb3.yaml

@@ -75,6 +75,7 @@ required:
   - reg
   - reg-names
   - interrupts
+  - interrupt-names
 
 additionalProperties: false