ASoC: msm: qdsp6v2: do not allow multiple instances of VoIP driver

Multiple instances of VoIP driver are not supported and when opened
multiple instances causing corruption in the VoIP data structure.
Add condition checks to handle invalid requests from userspace.

CRs-Fixed: 669865
Change-Id: I3f1b5cc0fb31ba76fbeb3d3e186bfcce49c3505a
Signed-off-by: Venkata Narendra Kumar Gutta <vgutta@codeaurora.org>