Fix RNG seed initialization when passed as a parameter

[meiniKi]

Fixes the rngstate assignment for DeterministicRNG when the seed is passed as a parameter. Assigning a seed of zero should be avoided as it leads to a constant zero output that can cause infinite loops, e.g.,

nextpnr/common/place/placer_static.cc

Lines 380 to 381 in 7c45980

	while (u1 < 1e-5)
	u1 = ctx->rngf(1.0f);