clk: ux500: prcc: constify clk_ops.

clk_ops are not supposed to change at runtime. All functions
working with clk_ops provided by <linux/clk-provider.h> work
with const clk_ops. So mark the non-const clk_ops as const.

Here, Function "clk_reg_prcc" is used to initialized clk_init_data.
clk_init_data is working with const clk_ops. So make clk_reg_prcc
non-const clk_ops argument as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>