[thermalsensor] Don't report wrongly suspicious temp readings. 

Thermal sensor was complaining unnecessarily about suspicious battery temp readings. This happened in normal conditions when device was suspended between readings and device temp slowly changed. Sw didn't check the time passed between these two readings. Now we limit that complain to readings that happen within two minutes suspend time included.

Signed-off-by: Pekka Lundstrom <pekka.lundstrom@jollamobile.com>
out of curiosity: is this just to be safe, or can previous_time actually be lower than current_time?