dt-bindings: watchdog: restrict node name suffixes

Make the pattern matching node names a bit stricter to improve DTS
consistency.  The pattern is restricted to -N suffixes to decimal
numbers.

Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lkml.kernel.org/r/20230530144851.92059-8-krzysztof.kozlowski@linaro.org


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>