Can you be more specific about the non-zero value? Is it the same every time? What happens if you send 0xFF?
If you can capture the logic analyzer trace, you might see something that makes more sense.
This is just Driver layer stuff (HAL) or are you using the Framework? There's an on-line guide to the SPI framework that can help here:
http://synergywiki.renesas.com/index.php/4.1.14.1_Framework_SPI_Interface_SSP_UM_v09
Note that it works with the RSPI and the "standard" SPI too. So you need to make sure you select the right modules in the HAL.