OPP: Check for invalid OPP in dev_pm_opp_find_level_ceil()

_find_key_ceil() may return an error and that must be checked before
passing the same to dev_pm_opp_put().

Fixes: 41907aa4ae37 ("OPP: Level zero is valid")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>