atusb/fw/boot.c: adjusted the delay loop and don't race with dfu-util
atusb/fw/boot.c: adjusted the delay loop and don't race with dfu-util

- boot.c (MS_TO_LOOPS): increased loop count now that we no longer
  have to poll
- boot.c (main): increased delay from 2.0 s to 2.5 s, because we were
  racing with a sleep(2) in dfu-util

cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan