Fix KoboLight sensitivity
Fix KoboLight sensitivity

Which was increasing after each opening of a document.
Closes #2605

robert00s/koreader,mwoz123/koreader,houqp/koreader,apletnev/koreader,lgeek/koreader,pazos/koreader,NiLuJe/koreader,koreader/koreader,koreader/koreader,Frenzie/koreader,Hzj-jie/koreader,mihailim/koreader,Frenzie/koreader,poire-z/koreader,poire-z/koreader,Markismus/koreader,NiLuJe/koreader