dooly: fix lux overflow
dooly: fix lux overflow

We saw under some low light environment
lux will switch between 0 to extreme high value,
wich will cause display backlight flash,
this CL fix this issue due there is overflow in calculation.

BUG=b:188205311
BRANCH=puff
TEST=make sure panel backlight not flash in low light environment.

Signed-off-by: Zick Wei <3d0b14a1e83601e71d11cd2c38ee93ff1dbbc737@quanta.corp-partner.google.com>

Change-Id: I47680e0c84d84f183fd5c2b973429e9964539049
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2909095
Tested-by: Zick Wei <3d0b14a1e83601e71d11cd2c38ee93ff1dbbc737@quanta.corp-partner.google.com>
Tested-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>
Reviewed-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>
Commit-Queue: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec