Add a description for spi_mem_op.data.nbytes to the kerneldoc header.
Fixes: c36ff266dc82 ("spi: Extend the core to ease integration of SPI memory controllers")
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
  * @dummy.buswidth: number of IO lanes used to transmit the dummy bytes
  * @data.buswidth: number of IO lanes used to send/receive the data
  * @data.dir: direction of the transfer
+ * @data.nbytes: number of data bytes to send/receive. Can be zero if the
+ *              operation does not involve transferring data
  * @data.buf.in: input buffer
  * @data.buf.out: output buffer
  */