clk: sunxi: Fix sun8i-a23-apb0-clk divider flags

The APB0 clock on A23 is a zero-based divider, not a power-of-two based
divider.

Note that this patch does not apply cleanly to kernels before 4.5-rc1,
which added CLK_OF_DECLARE support to this driver.

Fixes: 57a1fbf2 ("clk: sunxi: Add A23 APB0 divider clock support")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>