clk: sunxi: Specify number of child clocks for divs clocks

Currently sunxi_divs_clk_setup assumes the number of child clocks
to be the same as the number of clock-output-names, and a maximum
of SUNXI_DIVS_MAX_QTY child clocks.

On sun6i, PLL6 only has 1 child clock, but the parent would be used
as well, thereby also having it's own clock-output-names entry. This
results in an extra bogus clock being registered.

This patch adds an entry for the number of child clocks alongside
the data structures for them.

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