ARM: dts: kzm9d: Drop unnecessary address properties from gpio_keys node

The gpio_keys node does not have an address and thus does not need
address-cells or address size-properties.

This is flagged by dtc as follows:
 # make dtbs W=1
 arch/arm/boot/dts/emev2-kzm9d.dtb: Warning (avoid_unnecessary_addr_size): /gpio_keys: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>