prototype: Change USB to hex format

This is what all the specs are in and the decimal makes it impossible to
read.

BUG=None
TEST=None

Change-Id: I92e4cfa0b4dfec004452edbdeb3d58dce38e4d51
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/1989473
Reviewed-by: C Shapiro <shapiroc@chromium.org>
Commit-Queue: C Shapiro <shapiroc@chromium.org>
Tested-by: C Shapiro <shapiroc@chromium.org>
Auto-Submit: C Shapiro <shapiroc@chromium.org>
3 files changed