libstagefright: Fix app crash during pcm offload playback

 -ANR is seen with trick mode operations during
  pcm offload playback.
 -If Player issues the read request to omx client while omx client is
  in pausing state, it moves the client to executing state if variable
  mPasued is true and it never returns from pause.
 -Do not set the variable mPaused to true while it is in pausing state.

Change-Id: Ib824f3a651f738be26df8906d7175eb59ce82fab