msm: vidc: reduce max_packets count to 480

Currently max_packets is configured as 1000, but max outstanding
packets will not exceed more than 480(16 clients x 30 pkts/client).

Bug: 153501065
Test: camera recording/video playback
Change-Id: I57a302857ce143c8c7507818e6e9e9ed1e29f327
Signed-off-by: wenchangliu <wenchangliu@google.com>