clk: max-gen: Silence sparse warnings

drivers/clk/clk-max-gen.c:82:16: warning: symbol 'max_gen_clk_ops' was not declared. Should it be static?
drivers/clk/clk-max-gen.c:109:5: warning: symbol 'max_gen_clk_probe' was not declared. Should it be static?
drivers/clk/clk-max-gen.c:183:5: warning: symbol 'max_gen_clk_remove' was not declared. Should it be static?

Acked-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>