Revert "Allow brightness decrease when sensor value is zero"

Not needed in cm-10.1, reverting it allows us to use again the lowest brightness with 0 lux.

This reverts commit 591c7678b4f8ea615cbf07d410f31adbe4abdc09.

Signed-off-by: Michael Bestas <mikeioannina@gmail.com>

Change-Id: Id8b2ebbccf0851b753286b09e11d011e6bbb464a