Voldemort has some pretty good energy blasts at his disposal and most of them will instantly cause death to the average mortal. Lucifer is no mortal though and he is one of the tougher demons that Ghost Rider faced back in the day. His Hellfire should have an immediately lethal effect on Voldemort and no spell will save the villain at that point. In a battle between demons, the one with the larger fireblast may end up taking the edge, in most cases. Lucifer wins.