ASoC: dt-bindings: mediatek,mt2701-wm8960: Correctly use additionalProperties

ASoC: dt-bindings: mediatek,mt2701-wm8960: Correctly use additionalProperties

The binding does not reference any other schema, thus should use
"additionalProperties: false" to disallow any undocumented properties.
Correct the code and place this after "required:" block to match
convention expressed in example-schema.yaml.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260325110849.127051-3-krzysztof.kozlowski@oss.qualcomm.com
Signed-off-by: Mark Brown <broonie@kernel.org>