opp: Fix dev_pm_opp_set_rate() to not return early

dev_pm_opp_set_rate() can now be called with freq = 0 inorder
to either drop performance or bandwidth votes or to disable
regulators on platforms which support them.
In such cases, a subsequent call to dev_pm_opp_set_rate() with
the same frequency ends up returning early because 'old_freq == freq'
Instead make it fall through and put back the dropped performance
and bandwidth votes and/or enable back the regulators.

Fixes: cd7ea582 ("opp: Make dev_pm_opp_set_rate() handle freq = 0 to drop performance votes")
Reported-by: Sajida Bhanu <sbhanu@codeaurora.org>
Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>