dt-bindings: pinctrl: amlogic: narrow regex for unit address to hex numbers

Regular expression used to match the unit address part should not allow
non-hex numbers.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240123083511.21063-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>