lightsensor: fix insanely high bogus luxvalues in certain cases

e.g. for the case that cdata==1 and irdata==1 the calculations in the APDS block will result in 42949672 and LUX=15891374.
this is an unwanted bahavior which will eventually result in burning your eyeballs out of your skull (notionally) in low-light conditions by raising the backlight to 255.