Work around erroneous initial brightness reporting

In some devices the display brightness sysfs controls are out of sync
with reality after bootup. This can cause a) mce not to adjust the
brightness if reported level matches target b) kernel to ignore the
level set by mce unless the value differs from the reported. If either
happens the display can stay at boot default level until the display is
cycled off and on again or the brightness level in settings is changed.

Write reported value minus one to brightness control sysfs file on mce
startup. This makes kernel see a changed value (during bootup) without
affecting display brightness too much (mce restart while display is on).

Also make single step brightness adjustments happen immediately instead
of via fading timer.

[mce] Work around erroneous initial brightness reporting. Fixes JB#23138
Merge pull request #217 from spiiroin/initial_brightness

Work around erroneous initial brightness reporting