Based on tests with my left ear (which appears to require lower levels
than the right one), one Birch, one Dogwood and three Evergreens.

It seems that the sensor reacts very weakly to hair, so let's make
the thresholds rather generous to compensate.
Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>