/smb@8000000/motherboard/gpio_keys node doesn't have "ranges" or "reg"
property in child nodes. So it's unnecessary to have address-cells
as well as size-cells properties which results in below warning.

Warning (avoid_unnecessary_addr_size):
/smb@8000000/motherboard/gpio_keys:
	unnecessary #address-cells/#size-cells without "ranges" or child "reg"
	property

This patch drops the unnecessary address+size-cell properties.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>