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>