dt-bindings: gpio: st,nomadik-gpio: Add missing "#interrupt-cells" to example

Enabling dtc interrupt_provider check reveals the example is missing the
"#interrupt-cells" property as it is a dependency of
"interrupt-controller".

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240925173504.1906872-1-robh@kernel.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>