clk: constify of_device_id array

of_device_id is always used as const.
(See driver.of_match_table and open firmware functions)

__initdata updated to __initconst for
static const struct of_device_id ti_clkdm_match_table[]

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>