hwc: Invoke commit ioctl even if there are no app layers

  Android has scenarios where it calls HWC::prepare and HWC::set
  without any application layers. In such cases, for power
  optimization, user space avoids  calling PLAY
  (on FB - since there is no new content drawn) and COMMIT ioctls.
  But we might have called UNSET on mdp pipes used for the previous
  frame. As per the current MDP design, these freed pipes will not
  be unstaged unless atleast a COMMIT ioctl is called on that mixer.

Change-Id: I7f7574b2e589e80c4926533066e35784bb29b4a5
CRs-Fixed: 437736
1 file changed