dt-bindings: firmware: ixp4xx: Drop redundant minItems/maxItems

The minItems/maxItems default to the number of items in an 'items' list,
so drop the redundant specifying of them here.

Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/firmware/intel,ixp4xx-network-processing-engine.yaml

···
           - const: intel,ixp4xx-network-processing-engine
 
   reg:
-    minItems: 3
-    maxItems: 3
     items:
       - description: NPE0 register range
       - description: NPE1 register range