clk: sunxi: fix initialization of basic clocks

With the recent move towards CLK_OF_DECLARE(...), the driver stopped
initializing osc32k, which is compatible "fixed-clock". This is because
we never called of_clk_init(NULL). Fix this by moving the only other
simple clock (osc24M) to use CLK_OF_DECLARE(...) and call of_clk_init(NULL)
to initialize both of them.

Signed-off-by: Emilio López <emilio@elopez.com.ar>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Mike Turquette <mturquette@linaro.org>