clk: pxa: constify clk_ops structures

These clk_ops structures are only passed to a call to
clk_register_composite where the corresponding parameters
are const, so the clk_ops structure 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>