dt-bindings: mux: 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>
Acked-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20240109082511.15278-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Rob Herring <robh@kernel.org>