dts/st: dtc v1.4.6 warnings: #address-cells/#size-cells without "ranges"

To prepare to upcoming dtc v1.4.6, fix warnings in dts files.

This commit addresses the following warning:
"unnecessary #address-cells/#size-cells without "ranges" or child
"reg" property in /gpio_keys".

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>