media: venus: vdec: Mark flushed buffers with error state

Once the hfi_session_flush is issued by the vdec all queued
buffers to firmware should be returned to the v4l driver. Some
of those buffers are not processed at the time of flush command,
those buffers has filled len zero (no data). Catch that in
buffer_done callback and mark not filled capture buffers with
error state so that client can discard them.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>