msm: camera: reqmgr: Skip wd timer update if there is no valid request

At a given point if there is no request to apply, carry forward
the same timeout value for the wd timer. Modify timer only in
cases where we apply a valid request.

CRs-Fixed: 2698225
Change-Id: I92a1f1c6d0154349e19fdc1582d9d8836a7db1f4
Signed-off-by: Karthik Anantha Ram <kartanan@codeaurora.org>