clk: sunxi: rewrite sun8i-a23-mbus-clk using the simpler composite clk

sun8i-a23-mbus-clk used sunxi's factors clk, which is nice for very
complicated clocks, but is not really needed here.

Convert sun8i-a23-mbus-clk to use clk_composite, as it is a gate + mux
+ divider. This makes the code easier to understand.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>