arm64: dts: meson-gxm-khadas-vim2: fix gpio-keys-polled node

Fix DTC warnings:

meson-gxm-khadas-vim2.dtb: Warning (avoid_unnecessary_addr_size):
   /gpio-keys-polled: unnecessary #address-cells/#size-cells
	without "ranges" or child "reg" property

Fixes: b8b74dda

 ("ARM64: dts: meson-gxm: Add support for Khadas VIM2")
Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>