Here is the quote I pulled, broken down:
Whether they will or not, they cannot but know that these are proofs of his Godhead, and yet they inwardly suppress them.
Man knows, today, not just in the Garden, that what he is seeing is proofs of God's Godhead. I would even argue that the way Calvin has this worded that he means Man specifically knows it is the God of the Bible.
They have no occasion to go farther than themselves, provided they do not, by appropriating as their own that which has been given them from heaven, put out the light intended to exhibit God clearly to their minds.
God has intended to provide a light that will exhibit Himself clearly to Men's, all men's, minds. Not just spiritually alive Man, and not just Pre-Fall Man, but all Men today.
Then according to Calvin, Man's nature has snuffed that light out. Thereby thwarting a thing God has intended.
Do you think I am really that far off track with my interpretation of what Calvin has said?