dt-bindings: interrupt-controller: ti,sci-inta: 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".

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240925173432.1906168-1-robh@kernel.org


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