clk: moxart: Silence sparse warnings

drivers/clk/clk-moxart.c:18:13: warning: symbol 'moxart_of_pll_clk_init' was not declared. Should it be static?
drivers/clk/clk-moxart.c:56:13: warning: symbol 'moxart_of_apb_clk_init' was not declared. Should it be static?

Cc: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>