ARM: dts: sun4i: Fix gpio-keys warning

Fix the 'unnecessary #address-cells/#size-cells without "ranges" or child
"reg" property' DTC warning for the gpio-keys DT node on A10 boards.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>