diag: dci: Prevent task deallocation and possible resource leak

Prevent DCI clients' task structs from being deallocated to provide
diag driver a chance to clean up its dci client list. Also update
dci client list pid reference count properly to prevent any resource
leakage.

Change-Id: Ie15df7103ef1ec733e1e0d08a0a22b4da6b418b3
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>