msm: camera: reqmgr: Fix timing issue while destroying the session

During destroying the session, sof freeze timeout happens
after destroying workqueue. Then sof freeze timeout callback
will access workqueue causing use after free memory issue.
This change invokes destroying timer prior to workqueue.

CRs-Fixed: 2807936
Change-Id: I1f0dcb7a03fbf802f4ec872727e3b627a78f56f8
Signed-off-by: zhuo <zhuo@codeaurora.org>