ti-soc-thermal: Delete an unnecessary check before the function call "cpufreq_cooling_unregister"

The cpufreq_cooling_unregister() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>