I think this is a bug with debian 9, with debian 8 it works without this parameter. Searched a long time for this solution, finally i found this report which helps me: https://github.com/flashrom/flashrom/issues/29
Now i see that Nico changed it in the wiki. -> https://flashrom.org/RaspberryPi Thanks! Too bad he changed it not a week ago, that would have me much time saved. ;-) Think you can change it from 1000 to 30000 because it is much much faster and works stable.
Greets