altos/ao_rn4678: Send '$$$' for new devices. Fix name setting code.

New devices won't respond to the cmd pin we have configured, so get
them to command mode by sending the $$$ string. Somehow I'd botched
the name setting code and hadn't caught it as I hadn't tried a new
device...

Signed-off-by: Keith Packard <keithp@keithp.com>