Avrcp_ext: always clear isShoActive after a2dp becomes playing

Analysis:
1) One device is active, and a2dp is playing.
2) User sets active device to a new device, then startSHO will be
   called with PlayReq true, then isShoActive is set to true.
3) SHO is done, and a2dp becomes playing again. Because avrcp
   of the new active device is not connected, isShoActive cannot
   be cleared, which caused that all the following SHO will be
   equeued incorrectly.

Fix:
Always clear variable isShoActive after a2dp becomes playing
even though avrcp is not connected.

Change-Id: If898ab177e70533ce31f77df8437240e9a832988
CRs-Fixed: 2597340