clk: ingenic: Use const pointer to clk_ops in struct

clk: ingenic: Use const pointer to clk_ops in struct

The CGU common code does not modify the pointed clk_ops structure, so it
should be marked as const.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Maarten ter Huurne <maarten@treewalker.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18476/
Signed-off-by: James Hogan <jhogan@kernel.org>