Based on your question, you are looking to calculate the overall SNR to apply the correct amount of AWGN to the signal to produce a bit error rate curve. Also I will assume that the EbNo is the EbNo per OFDM subcarrier.
The coding rate is defined as the message length divided by the code length, so it appears you have that accounted for twice in your equation. I believe the "10*log10(K/N)" is redundant, since it is covered by "Coding Rate" and should be removed.
Also, cyclic prefix should not be included in the calculation. This is because the receiver will immediately remove samples related to the cyclic prefix when demodulating the signal. Because the receiver never sees the energy of those samples in the cyclic prefix, it should not count towards the SNR. So the last term in your equation should be removed as well.
You can refer to the documentation on the Communictions Toolbox function convertSNR (convertSNR) to see more of an explanation on how EbNo is calculated. Also, there is an explanation for how SNR is calculated in multicarrier (OFDM) systems. You have correctly included the "+10*log10(DC/NFFT)" factor in your calculation (this assumes that all subcarriers are transmitting at the same power) to account for the possibility that not all subcarriers will be filled with energy.
Finally, it is not necessary to compute the linear SNR value for the awgn function. By default, the awgn function accepts SNR in dB, so you may use this instead:
awgnChanOut = awgn(OFDM_TX_serial,snr_tot_dB,'measured');
