Yosys 0.44 driver-driver conflict; Verilator 5.028 & Yosys process all cases differently

Yosys 0.44 gets driver-driver conflict with 'reg R1', 'reg R2', 'reg R3' and 'reg R4' (from 'mux.v') and 'resolves' this conflict by replacing them with wires and assigning them constant values resulting in the discrepancy of the simulation results.

Also need initialization of 'reg R1', 'reg R2', 'reg R3' and 'reg R4' to avoid possible discrepancy of the simulation results.

Signed-off-by: Ivan Grigorov grigorovia@ispras.ru