spi: Doc fix - Describe add_lock and dma_map_dev in spi_controller

This fixes the corresponding warnings during building the docs.

Signed-off-by: Siddh Raman Pant <siddhpant.gh@gmail.com>
Link: https://lore.kernel.org/r/4e6187a4-d0f8-4750-e407-e09cc1c91789@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi.h

@@ -347,6 +347,7 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  * @max_message_size: function that returns the max message size for
  *	a &spi_device; may be %NULL, so the default %SIZE_MAX will be used.
  * @io_mutex: mutex for physical bus access
+ * @add_lock: mutex to avoid adding devices to the same chipselect
  * @bus_lock_spinlock: spinlock for SPI bus locking
  * @bus_lock_mutex: mutex for exclusion of multiple callers
  * @bus_lock_flag: indicates that the SPI bus is locked for exclusive use
@@ -361,6 +362,7 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  * @transfer: adds a message to the controller's transfer queue.
  * @cleanup: frees controller-specific state
  * @can_dma: determine whether this controller supports DMA
+ * @dma_map_dev: device which can be used for DMA mapping
  * @queued: whether this controller is providing an internal message queue
  * @kworker: pointer to thread struct for message pump
  * @pump_messages: work struct for scheduling work to the message pump