device/kobo/sysfs_light: Make used exponent in formulas a variable
device/kobo/sysfs_light: Make used exponent in formulas a variable

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