diag: Assign dci_client_id properly while client registration

Currently while doing dci client registration dci_client_id is
assigned by incremeting previous id. Starting dci clients
multiple times can make id equal to error types and dci client
registratin can fail. The patch assign dci_client_id properly
and un-assign it while deinit of client.

Change-Id: Idd13166f5edb680f8c97c538a76ce613af3a1e8e
Signed-off-by: Hardik Arya <harya@codeaurora.org>