diag: dci: Fix timestamps on dci events

The first event generated by diag on the peripherals will have a
valid timestamp bytes and the subsequent events generated at the
same time will have reduced timestamp bytes to conserve
space in the buffer. Diag driver zeroed out the timestamp bytes
when it encounters DCI events with reduced timestamp bytes. This
patch adds the valid timestamp for those events.

Change-Id: I80b1a7450f605af9bfd8959ea1f26bc9d83b370e
CRs-Fixed: 521415
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>