FASTBOOT: Don't allow cmd_fastboot to be run twice

It's possible to make it work, but it's not a typical
path and we'd rather make it an error than add
support for it when it's going to be rarely used
and will probably be fragile.

Change-Id: I9a6f801a37c1cbe6e8c69ba6eb132d3ec116baa8
Signed-off-by: Mike J. Chen <mjchen@google.com>
2 files changed