backend/genesys: Increase excessively low bright point on Lide 80 calib

It looks like the bright point for Lide80 is calibrated too low which results in needlessly dark images. I've captured several color scans of white paper sheets with different bright point levels using the following command and took their histograms:

../bin/scanimage --format=png -y 100 --threshold=90 --resolution=900 --calibration-file lide80.cal --expiration-time=0  \
    --mode=Color --clear-calibration >out.png

Level 0xd000 (original)

Level 0xe000 (this PR)

Level 0xf000

As you can see, using 0xe000 bright point level increases the maximum color levels of images captured with default settings without excessive clipping.