diag: dci: Add protection while de-initializing clients

Currently, while de-initializing dci clients, there is
a possibility to access stale entries. This patch fixes
this issue by adding proper protection mechanism.

CRs-Fixed: 960958 968445
Change-Id: I829c9497eeb356662a6531592c66108e615ce6e4
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>