diag: dci: Validate dci client entries prior to access

The patch validates the dci entries and its task
structure before accessing structure members avoiding possible
kernel bug.

CRs-Fixed: 2035140
Change-Id: I7b0813defef1cb60400184acc631047cf72af94e
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>