dt-bindings: arm: fix typos in compatible

Fix typo "cortex"

Signed-off-by: Ken Kurematsu <k.kurematsu@nskint.co.jp>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/OSBPR01MB32880CB4C49E50DAB7C6B664DBC89@OSBPR01MB3288.jpnprd01.prod.outlook.com