libstagefright/omx: Fix logic to handle dead observers.

  OMXNodeInstance freeNode tries to tear down OMX component
  if not in OMX_StateLoaded. It handles all other states except
  OMX_StatePause. This change adds OMX_StatePause handling.

Change-Id: I3bae2015c57b932186069756490c9bdf1f93eea4