Attempt at sanitizing usb_write sanity check
Standardize device ID used in command line options.

Zeus driver now matches the behaviour of the Gridseed
driver. When using '--zeus-options' the ID can be the
serial number or the trailing part of the device path
(ttyUSB0 instead of /dev/ttyUSB0).

For backward compatibility full paths are still accepted
as IDs with '--zeus-options'.
Silence compiler warning