clk: ti: Mark ti_clk_features static

This variable isn't exported outside of this file so mark it
static. Silences the following sparse warning:

drivers/clk/ti/clk.c:36:24: warning: symbol 'ti_clk_features' was not declared. Should it be static?

Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>