The current code only rely on the parent to change its rate in the case
where CLK_SET_RATE_PARENT is set.

However, some clock rates might be obtained only through a modification of
the parent and the clock divider. Just rely on the round rate of the clocks
to give us the best computation that might be achieved for a given rate.

round_rate functions now need to honor CLK_SET_RATE_PARENT, but either the
functions already do that if they modify the parent, or don't modify the
praents at all.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>