IMO, this is poll is about as meaningful on CNN as if they put it on the NRA site. They are playing to their audience.
I have little to no faith in the media, their polls, their reporting. Just go to google news and see how different media outlets report the same story. Look for any listing of articles on the case before the supreme court.
Here are some sample headlines:
"Supreme Court, gun control, and the Second Amendment: a reckoning"
"Daley fires blanks on the Chicago gun ban"
"Preserving the right to regulate guns"
"Gun control"
"Supreme Court Weighs Chicago's Strict Gun Ban"
They will say whatever they want to sell paper, get ad revenue, etc.
It does not hurt or take more than a second to vote in the poll so I would go ahead and do so but I do not hold much stock in the outcome of said poll.