asoc: msm: Check headset insertion for consistency

 * It's possible to get a noisy reading during polling when
   transitioning to PLUG_TYPE_HEADSET. Poll again to double
   check that it's really a headset.
 * This helps when music is at full volume and a headphone
   is inserted. Double-checking the reading vastly improves
   the case where a noisy reading causes a mic to be detected.

Change-Id: I6e0863a46cdfd5316d798bc9b8348927fa403890