diag: dci: Safeguard to prevent Integer overflow

At certain point in diag driver there can be integer overflow
thus can lead to memory leak. Added a safeguard for it.

Change-Id: I80a9cd0623ebb84d82cf74de132211b1dd60c7d4
CRs-fixed: 565160
Signed-off-by: Katish Paran <kparan@codeaurora.org>