PM / OPP: Drop RCU usage in dev_pm_opp_adjust_voltage()

PM / OPP: Drop RCU usage in dev_pm_opp_adjust_voltage()

BugLink: http://bugs.launchpad.net/bugs/1763040
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
(cherry picked from commit 97c58e3fefb76f8e0cc7c2b8ee73d9d704f917f3
http://git.linaro.org/landing-teams/working/qualcomm/kernel.git release/qcomlt-4.14)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>