I agree, more or less - this is Carson’s fight, and Trump should keep out of it ... OTOH, if Carson lost a sufficient number of support b/c of this action - and those votes went to Cruz, it is possible that either the percentages for Trump and Cruz would have been much tighter - or that Trump may actually have squeaked ahead of Cruz ... In that context, Trump does have an argument.
I’m not stating that Trump would have won if not for this dirty trick, but I am suggesting that Trump does have standing.
Standing for what? Unless you could prove that the Cruz campaign deliberately fed CNN a false story and then used that false story to deceive the voters, you have no case. The story originated with the Carson campaign. CNN broadcast the story. The Cruz campaign used the story to try to win over voters. Nothing unethical, illegal or immoral about it.