The children of gpio_keys node do not have reg/ranges properties so remove
address-cells and size-cells properties.  This fixes warnings for
Exynos4210 Origen:

    arch/arm/boot/dts/exynos4210-origen.dtb: Warning (avoid_unnecessary_addr_size):
        /gpio_keys: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>