clk: pistachio: constify clk_ops structures

These clk_ops structures are only stored in the ops field of a
clk_init_data structure.  This field is const, so the clk_ops
structures can be const as well.

Identified and transformed using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>