ARM: dts: Add max77686 RTC interrupt to cros5250-common

Without the interrupt you'll get problems if you enable
CONFIG_RTC_DRV_MAX77686.  Setup the interrupt properly in the device
tree.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: stable@vger.kernel.org