clk: mediatek: Drop __initconst from gates

In the Linux kernel, the following vulnerability has been resolved: clk: mediatek: Drop __initconst from gates Since commit 8ceff24a754a ("clk: mediatek: clk-gate: Refactor mtk_clk_register_gate to use mtk_gate struct") the mtk_gate structs are no longer just used for initialization/registration, but also at runtime. So drop __initconst annotations.