clk: divider: Fix best div calculation for power-of-two and table dividers

The divider returned by clk_divider_bestdiv() is likely to be invalid in case
of power-of-two and table dividers when CLK_SET_RATE_PARENT flag isn't set.

Fixes boot on STiH416 platform.

Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
[mturquette@linaro.org: trivial merge conflict & updated changelog]