dt-bindings: touchscreen: resistive-adc-touch: change to unevaluatedProperties

Change additionalProperties to unevaluatedProperties because it refs to
touchscreen.yaml.

Fix below CHECK_DTBS warnings:
arch/arm/boot/dts/nxp/imx/imx6dl-skov-revc-lt6.dtb: touchscreen (resistive-adc-touch): 'touchscreen-y-plate-ohms' does not match any of the regexes: '^pinctrl-[0-9]+$'
	from schema $id: http://devicetree.org/schemas/input/touchscreen/resistive-adc-touch.yaml#

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250910224402.994046-1-Frank.Li@nxp.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: nxpfrankli

Documentation/devicetree/bindings/input/touchscreen/resistive-adc-touch.yaml

@@ -55,7 +55,7 @@ properties:
   touchscreen-min-pressure: true
   touchscreen-x-plate-ohms: true
 
-additionalProperties: false
+unevaluatedProperties: false
 
 required:
   - compatible