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).

Change-Id: I8c074e08c959473c20450bc7d62486362ba81b47
Signed-off-by: Govindaraj Rajagopal <grajagop@codeaurora.org>