thermal/cpu_cooling: convert 'switch' block to 'if' block in notifier

We just need to take care of single event here and there is no need to
increase indentation level of most of the code (which causes lines
longer that 80 columns to break).

Kill the switch block.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>