dt-bindings: PCI: snps,dw-pcie: Drop "#interrupt-cells" from example

"#interrupt-cells" is not valid without a corresponding "interrupt-map"
or "interrupt-controller" property. As the example has neither, drop
"#interrupt-cells".

This fixes a dtc interrupt_provider warning.

Link: https://lore.kernel.org/r/20241105213217.442809-1-robh@kernel.org


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