diag: dci: Index DCI client table by client ID

Diag driver maintains a table of all DCI clients. This table
is currently indexed by the PID of the clients. Make changes to
index the table based on an unique client ID.

Change-Id: I28a95aac3aa47b1c35190f3048bbd9103c884adb
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>