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

Documentation/devicetree/bindings/arm/bcm/brcm,bcm63138.txt

@@ -30,7 +30,7 @@ Example:
 
 	cpus {
 		cpu@0 {
-			compatible = "arm,cotex-a9";
+			compatible = "arm,cortex-a9";
 			reg = <0>;
 			...
 			enable-method = "brcm,bcm63138";