camera3_test: fix metadata updating parameter

Fix the data_count parameter of metadata updating, which should be a
count, instead of size, of the data.

BUG=b/32689987
TEST='emerge-elm arc-camera3-test'
     'sudo -u arc-camera -g arc-camera /usr/bin/arc_camera3_test'

Change-Id: I0aa712e723cb4735701638634b119c11361eef41
Reviewed-on: https://chromium-review.googlesource.com/582711
Commit-Ready: Hung-yu Wu <hywu@chromium.org>
Tested-by: Hung-yu Wu <hywu@chromium.org>
Reviewed-by: Heng-ruey Hsu <henryhsu@chromium.org>
3 files changed