spi.h: add missing kernel-doc for struct spi_master

Add missing kernel-doc notation in spi.h for struct spi_master:

Warning(include/linux/spi/spi.h:289): No description found for parameter 'mode_bits'
Warning(include/linux/spi/spi.h:289): No description found for parameter 'flags'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/spi/spi.h

@@ -207,6 +207,8 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
  *	each slave has a chipselect signal, but it's common that not
  *	every chipselect is connected to a slave.
  * @dma_alignment: SPI controller constraint on DMA buffers alignment.
+ * @mode_bits: flags understood by this controller driver
+ * @flags: other constraints relevant to this driver
  * @setup: updates the device mode and clocking records used by a
  *	device's SPI controller; protocol code may call this.  This
  *	must fail if an unrecognized or unsupported mode is requested.