msm: qdsp5: Exit VOIP thread at the end of MVS session

In the MVS open, a thread is created but the same is not getting exited
during the MVS release
Added logic to exit the thread in the release.

CRs-Fixed: 395518
Change-Id: If408fde85eab629b46fa08514ccb57d2ce6e3b95
Signed-off-by: Vinay Vaka <vvaka@codeaurora.org>