thermal: cpu_cooling: Remove cpu_dev update on policy CPU update

It was initially understood that an update to the cpu_device
(cached in cpufreq_cooling_device) was required to ascertain the
correct operating point of the device on a cpufreq policy->cpu update
or creation or deletion of a cpufreq policy.
(e.g. when the existing policy CPU goes offline).

This update is not required and it is possible to ascertain the OPPs
from the leading CPU in a cpufreq domain even if the CPU is hotplugged out.

Fixes: e0128d8ab423 ("thermal: cpu_cooling: implement the power cooling device API")
Acked-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: Kapileshwar Singh <kapileshwar.singh@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>