CLK: SPEAr: make structure field and function argument as const

Make the masks field of clk_aux structure const as it do not modify the
fields of the aux_clk_masks structure it points to.

Make the struct aux_clk_masks *aux argument of the function
clk_register_aux as const as the argument is only stored in the masks
field of a clk_aux structure which is now made const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>