dt-bindings: rtc: isl12022: add #clock-cells property

The isl12022 has a dual-purpose irq/f_out pin, which can either be
used as an interrupt or clock output.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230615105826.411953-8-linux@rasmusvillemoes.dk


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>