dt-bindings: thermal: Fix false warning with 'phandle' in trips nodes

dt-bindings: thermal: Fix false warning with 'phandle' in trips nodes

A pattern property matching essentially anything doesn't work if there
are implicit properties such as 'phandle' which can occur on any node.
One such example popped up recently:

arch/arm64/boot/dts/qcom/sm8650-hdk.dtb: thermal-zones: gpuss0-thermal:trips:phandle: 531 is not of type 'object'
        from schema $id: http://devicetree.org/schemas/thermal/thermal-zones.yaml

Instead of a pattern property, use an "additionalProperties" schema
instead which is the fallback in case of no matching property.

Link: https://patch.msgid.link/20260410223601.1487473-2-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>