audioflinger: Fix pops in LPA while effects are applied

 -Issue: LPA playback while effect are applied, has pops/noise
  as below scenarios
  1) LPA Playback + taking snapshot with camera
  2) LPA Playback + changing media volume from settings app
  3) LPA plaback after non-LPA playback
 -Rootcause:Effects meant for LPA are getting applied in
  normal playback path
 -Fix: In threadloop of mixerthread if current effect
  chain is equal to LPAeffectchain, don't apply effects.

CRs-Fixed: 526799

Change-Id: Ic255ef2db81545abd119633e8fc6a7bae5d2f38c