Since the spec says we Shall request no more power than we actually
need, we were violating the spec whenever the output was disabled in
Setup mode. This commit fixes that, requesting low current at 5 V when
the output is disabled.
We do play a little fast and loose with the MAX_CURRENT field, but
that's hard to avoid in a device like this. Well, we could always set
it to 5 A in Setup mode to be safe, but that's not necessarily right
either. At least it's still honest in Sink mode, which I consider more
important anyway.