Remove calloc from L1 at CSIRS_PDU conversion function
Remove calloc from convert_csirs_pdu function, change return value from 'nfapi_nr_dl_tti_csi_rs_pdu_rel15_t *' to 'nfapi_nr_dl_tti_csi_rs_pdu_rel15_t' to not require call to 'free()'. This is a fix for MR2369, in which there is a calloc and not a call to free().