clk: sunxi: Make clocks setup functions return their clock

The clocks registration code in clk-sunxi was most of the time not
returning the struct clk (or struct clk array) that was registered,
preventing the users of such functions to manipulate it, for example to
protect it.

Make them return it so that we can start using it.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>