PM / devfreq: Fix error handling in governor_cpufreq

put_online_cpus() is not called if an error occurs during cpufreq
notification registration. Fix the error path by calling it properly.

Change-Id: Ia2e6b2debb2db4b39f8fcfcd1ee873538b44d405
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>