spi: <linux/spi/spi.h>: add missing struct kernel-doc entry

Fix kernel-doc warning in spi.h by adding the missing kernel-doc entry
and also correct the original comment so that they both indicate the
correct polarity of the flag.

../include/linux/spi/spi.h:673: warning: Function parameter or member 'devm_allocated' not described in 'spi_controller'

Fixes: 794aaf01 ("spi: Fix use-after-free with devm_spi_alloc_*")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: William A. Kennington III <wak@google.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: linux-spi@vger.kernel.org
Cc: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/20210628210520.5712-1-rdunlap@infradead.orgSigned-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi.h

@@ -339,6 +339,7 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  * @max_speed_hz: Highest supported transfer speed
  * @flags: other constraints relevant to this driver
  * @slave: indicates that this is an SPI slave controller
+ * @devm_allocated: whether the allocation of this struct is devres-managed
  * @max_transfer_size: function that returns the max transfer size for
  *	a &spi_device; may be %NULL, so the default %SIZE_MAX will be used.
  * @max_message_size: function that returns the max message size for
@@ -511,7 +512,7 @@ struct spi_controller {
 
 #define SPI_MASTER_GPIO_SS		BIT(5)	/* GPIO CS must select slave */
 
-	/* flag indicating this is a non-devres managed controller */
+	/* flag indicating if the allocation of this struct is devres-managed */
 	bool			devm_allocated;
 
 	/* flag indicating this is an SPI slave controller */