Hi. The warnings could be caused by various things. As you provided very little information of the tools you are using, I can’t really guess. This sample project was done some few years ago, a lot has change since then: new FatFs versions, New MCC versions, new MPLAB X IDE versions, new XC8 versions especially the new v2.
And warnings are not necessarily gonna make your project not to work.
Are you testing already with hardware?
The SPI low level functions are handled by MCC. Check the SPI.C and SPI.h files generated by MCC. They’ve got nothing to do with FatFs.