clk: mvebu: Staticize of_cpu_clk_setup

'of_cpu_clk_setup' is used only in this file. Make it static.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>