sow.py: clean up seedpos magic number
sow.py: clean up seedpos magic number

Signed-off-by: John McMaster <527ca5438b47432dedda4309be2f991b71bfb11c@gmail.com>

SymbiFlow/fpga-tool-perf,SymbiFlow/fpga-tool-perf,SymbiFlow/fpga-tool-perf,SymbiFlow/fpga-tool-perf