clk: Remove clk_init_cb typedef

Since commit c08ee14c ("clk: ti: change clock init to use
generic of_clk_init"), there is only a single (private) user left of the
(public) clk_init_cb typedef.

Hence expand its single user in the core clock code, and remove the
typedef.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/1523365565-17124-1-git-send-email-geert+renesas@glider.be