dt-bindings: PCI: rockchip,rk3399-pcie: Add missing maxItems to ep-gpios

dt-bindings: PCI: rockchip,rk3399-pcie: Add missing maxItems to ep-gpios

Properties with GPIOs should define number of actual GPIOs, so add
missing maxItems to ep-gpios.  Otherwise multiple GPIOs could be
provided which is not a true hardware description.

Fixes: aa222f9311e1 ("dt-bindings: PCI: Convert Rockchip RK3399 PCIe to DT schema")
Link: https://lore.kernel.org/linux-pci/20240401100058.15749-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>