ab8500_fg: Don't clear the CCMuxOffset bit

The CCMuxOffset bit is not kept set. This will force the
columb counter of the AB8500 to use the measure offset
calibration. This should increase the accuracy of the fuel
gauge.

Signed-off-by: Kalle Komierowski <karl.komierowski@stericsson.com>
Signed-off-by: Marcus Cooper <marcus.xm.cooper@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Jonas ABERG <jonas.aberg@stericsson.com>