Fix HTC headset handling.

HTC's headset driver adds additional bits to the switch state, which
we're unable to deal with. Fix that by masking out those bits and
keeping only the valid ones.

Change-Id: I29f0de9520ebb56d61acbc9a6dfcfc73e1f297d8
Merge "Fix HTC headset handling." into cm-10.1
Merge remote branch 'cm/cm-10.1' into cm-10.1