dsp: lsm: move lsm_common deregister out of mutex_lock

When dispatch_event in apr and q6lsm_client_free in q6lsm
are running concurrently, there may be deadlock between
session_lock in lsm and svc->m_lock in apr for lsm_common.
Move lsm_common mmap apr deregister out of mutex_lock to
avoid deadlock.

Change-Id: I7c96ba12834bd4a7c8e5ca1b78d798578678b251
Signed-off-by: Meng Wang <mengw@codeaurora.org>