msm: clock-generic: Return best parent_rate from div_round_rate

Returning only the rounded rate and corresponding divider is not
sufficient. Since these values must be represented as integers, rather
than fractions, their product may not be equal to the actual parent
clock rate necessary.

Change-Id: I16a18595baa6f12d3fb3f7379acc80ee3988b2a3
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>