Input: qt2160 - fix qt2160_write() implementation

The previous implementation of qt2160_write() didn't work properly because
the value was actually not written to the device. Probably nobody detected
this because the only write that was issued was the one related to auto
calibration.

In order to fix the problem use a similar aproach as qt1070 instead.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>