msm: vidc: Fix timestamp for EOS buffer

Timestamp for zero filled length FBD is not
being set correctly even if the timestamp from FW
is valid. This causes certain decode usecase
to not exit correctly.

CRs-fixed: 664086
Change-Id: Ieb0f274efa5d94c9294b021e061bca6d9b45de87
Signed-off-by: Sachin Shah <sachins@codeaurora.org>