parallel-nextpnr-nexus: better seed handling
parallel-nextpnr-nexus: better seed handling

Uses the incoming seed as the first seed rather then always starting
from 1000.

Signed-off-by: Alan Green <97e77871b5fcc4941bebceb4338c97c1fd149f8c@google.com>

google/CFU-Playground,google/CFU-Playground,google/CFU-Playground,google/CFU-Playground