thermal/drivers/cpu_cooling: Remove pointless test in power2state()

When the static power computation was removed, the test with the power
being negative was not removed. However, the substraction which was
responsible of the negative value was removed and the variable is now
an u32. A double reason to remove the test which does not make sense.

Fixes: 84fe2cab ("cpu_cooling: Drop static-power related stuff")
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>