arm64: dts: mediatek: align thermal zone node names with dtschema

Align the name of thermal zone node to dtschema to fix warnings like:

  arch/arm64/boot/dts/mediatek/mt8173-elm.dt.yaml:
    thermal-zones: 'cpu_thermal' does not match any of the regexes: '^[a-zA-Z][a-zA-Z0-9\\-]{1,12}-thermal$', 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20210820081616.83674-2-krzysztof.kozlowski@canonical.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>