clk: mxs: Fix sparse warnings

Fix the following sparse warnings:

drivers/clk/mxs/clk.c:17:1: warning: symbol 'mxs_lock' was not declared. Should it be static?
drivers/clk/mxs/clk.c:19:5: warning: symbol 'mxs_clk_wait' was not declared. Should it be static?

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>