Consider CQI as something like saying that for codeword 0 I am expecting to be able to decode transport block of size X at MCS Y within a bler of 10 percent.
Hence CQI is not reported for individual antennas as transport block is basically coded via the Codewords.
We have only 2 defined so CQI is reporter for max 2 CW no matter you use 4 layers or 8 in the downlink (Tm9 like BF).