dt-bindings: watchdog: Restrict timeout-sec to one number

Linux kernel expects only one number for the watchdog timeout and the
type is an array (defined in property-units.yaml in DT schema), so
restrict the property.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Author: krzk

Documentation/devicetree/bindings/watchdog/watchdog.yaml

@@ -24,6 +24,7 @@ properties:
     pattern: "^(timer|watchdog)(@.*|-([0-9]|[1-9][0-9]+))?$"
 
   timeout-sec:
+    maxItems: 1
     description:
       Contains the watchdog timeout in seconds.