PM / OPP: Hold dev_opp_list_lock for writers

Writers need to update OPP device and their list with dev_opp_list_lock
mutex held, which was missed at few places. Fix it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: 4.3 <stable@vger.kernel.org> # 4.3
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>