audioflinger: Handle pause /resume in stopping state

-Pre-requisite:
 Perform seek on the clip. After seek the data remaining till EOS
 is little more than the driver and common block buffering.
-Framework state:
 Offload thread is waiting for signal from the HAL for a free
 buffer. Audio Player calls sink stop on reaching EOS. Audio
 track is waiting on obtain buffer for a free space in common
 block to send the last buffer. The track is moved to stopping
 state as input EOS is reached.
-Issue:
 Perform pause/ resume in this state(STOPPING), Audio playback
 does not resume.
-Fix
 Ensure resume is called in stopping state if frames ready is
 greater than zero.

Change-Id: I9268ab2a6cd1cc69a3ff23801f978f7a9f75a11b