Make LED breathing less cpu intensive

Updating led brightness 50 times / second takes about 4% of cpu time.

Updating brightness 20 times / second and skipping sysfs writes that
would not change the led brightness cuts cpu usage to 1-2 % range
depending on lightning and number of led channels used for breathing.

[hybris.so] Make LED breathing less cpu intensive. Fixes JB#21501
Merge pull request #14 from spiiroin/breathing_cpu_use

Make LED breathing less cpu intensive