clk: exynos5420: Staticize local symbols

Symbols referenced only in this file are made static.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>