thermal: cpu_cooling: Check OPP for errors

It is possible for dev_pm_opp_find_freq_exact() to return errors. It was
all fine earlier as dev_pm_opp_get_voltage() had a check within it to
check for invalid OPPs, but dev_pm_opp_put() doesn't have any similar
checks and the callers need to make sure OPP is valid before calling
them.

Also update the later dev_warn_ratelimited() to not print the error
message as the OPP is guaranteed to be valid now.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>