msm: camera: reqmgr: Add protection while destroying the link

This change handles a race while destroying session. Protecting the
session destroy with session lock.

CRs-Fixed: 2799907
Change-Id: Ia1f90a56f6bfed00439b8012e41bfae9e8f739a3
Signed-off-by: Vikram Sharma <vikramsa@codeaurora.org>