PM / OPP: do error handling at the bottom of dev_pm_opp_add_dynamic()

This makes it less error prone and moves common resource deallocation at a
single place.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit 6ce4184d0308888dd6ac2b6ab5f8ec0b2006092e)
Signed-off-by: Alex Shi <alex.shi@linaro.org>