ARM: dts: replace number by macro in clock binding for exynos5420

sss module device node missed clock macro.
This patch replace magic number with macro in clock
binding for exynos5420.

Signed-off-by: Beomho Seo <beomho.seo@samsung.com>
Reviewed-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/boot/dts/exynos5420.dtsi

@@ -759,7 +759,7 @@
 		compatible = "samsung,exynos4210-secss";
 		reg = <0x10830000 0x10000>;
 		interrupts = <0 112 0>;
-		clocks = <&clock 471>;
+		clocks = <&clock CLK_SSS>;
 		clock-names = "secss";
 		samsung,power-domain = <&g2d_pd>;
 	};