If you are doing a literature review as a preliminary section before collecting data for a study then your literature review is not termed "secondary source of data". While all cited sources in this section are all secondary data, but in as much as it is not what you are presenting as your result that would be analysed, then it's not secondary data source
However, if the entire piece article being written by you is 'literature review' as in systematic literature review (SLR), Bibliometrics etc, then since its only the literature gathered that is presented and analysed, then the literature becomes a secondary data source