dt-bindings: pinctrl: nuvoton,npcm845: Add missing additionalProperties on gpio child nodes

Just as unevaluatedProperties or additionalProperties are required at
the top level of schemas, they should (and will) also be required for
child node schemas. That ensures only documented properties are
present for any node. Add the missing addtionalProperties to the 'gpio'
child nodes.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20231020170017.3610978-1-robh@kernel.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>