msm: audio: qdsp6v2: Don't reset mmap ref_cnt in RESET_EVENT

Only session open/close should increment/decrement mmap ref_cnt.
On receiving RESET_EVENT, mmap ref_cnt should not be reset to zero.
There could be open sessions when RESET_EVENT is received. The mmap
ref_cnt for open sessions will be decremented when user space issues
close for corresponding open sessions.

Change-Id: I3bfc7cebf11b8d363d11af2a938625d926a21788
Signed-off-by: Ravishankar Sarawadi <crsaraw@codeaurora.org>