ARM: dts: add 'rtc_src' clock to rtc node for exynos4412-odroid boards

The Exynos4412 SoC has a s3c6410 RTC where the source clock
is now a mandatory property.
This patch fixes probe failure of s3c-rtc on Odroid-X2/U2/U3 boards.
Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Tested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>

arch/arm/boot/dts/exynos4412-odroid-common.dtsi

@@ -9,6 +9,7 @@
 
 #include <dt-bindings/sound/samsung-i2s.h>
 #include <dt-bindings/input/input.h>
+#include <dt-bindings/clock/maxim,max77686.h>
 #include "exynos4412.dtsi"
 
 / {
@@ -105,6 +106,8 @@ watchdog@10060000 {
 
 	rtc@10070000 {
 		status = "okay";
+		clocks = <&clock CLK_RTC>, <&max77686 MAX77686_CLK_AP>;
+		clock-names = "rtc", "rtc_src";
 	};
 
 	g2d@10800000 {