spi: Remove unused function spi_busnum_to_master()

The last user is gone since commit

	2962db71 ("staging/fbtft: Remove fbtft_device")

in 2019.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211007121415.2401638-3-u.kleine-koenig@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/spi/spi-summary.rst

@@ -336,14 +336,6 @@ certainly includes SPI devices hooked up through the card connectors!
 Non-static Configurations
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Developer boards often play by different rules than product boards, and one
-example is the potential need to hotplug SPI devices and/or controllers.
-
-For those cases you might need to use spi_busnum_to_master() to look
-up the spi bus master, and will likely need spi_new_device() to provide the
-board info based on the board that was hotplugged.  Of course, you'd later
-call at least spi_unregister_device() when that board is removed.
-
 When Linux includes support for MMC/SD/SDIO/DataFlash cards through SPI, those
 configurations will also be dynamic.  Fortunately, such devices all support
 basic device identification probes, so they should hotplug normally.

drivers/spi/spi.c

@@ -3033,41 +3033,6 @@ int spi_controller_resume(struct spi_controller *ctlr)
 }
 EXPORT_SYMBOL_GPL(spi_controller_resume);
 
-static int __spi_controller_match(struct device *dev, const void *data)
-{
-	struct spi_controller *ctlr;
-	const u16 *bus_num = data;
-
-	ctlr = container_of(dev, struct spi_controller, dev);
-	return ctlr->bus_num == *bus_num;
-}
-
-/**
- * spi_busnum_to_master - look up master associated with bus_num
- * @bus_num: the master's bus number
- * Context: can sleep
- *
- * This call may be used with devices that are registered after
- * arch init time.  It returns a refcounted pointer to the relevant
- * spi_controller (which the caller must release), or NULL if there is
- * no such master registered.
- *
- * Return: the SPI master structure on success, else NULL.
- */
-struct spi_controller *spi_busnum_to_master(u16 bus_num)
-{
-	struct device		*dev;
-	struct spi_controller	*ctlr = NULL;
-
-	dev = class_find_device(&spi_master_class, NULL, &bus_num,
-				__spi_controller_match);
-	if (dev)
-		ctlr = container_of(dev, struct spi_controller, dev);
-	/* reference got in class_find_device */
-	return ctlr;
-}
-EXPORT_SYMBOL_GPL(spi_busnum_to_master);
-
 /*-------------------------------------------------------------------------*/
 
 /* Core methods for SPI resource management */

include/linux/spi/spi.h

@@ -760,8 +760,6 @@ extern int devm_spi_register_controller(struct device *dev,
 					struct spi_controller *ctlr);
 extern void spi_unregister_controller(struct spi_controller *ctlr);
 
-extern struct spi_controller *spi_busnum_to_master(u16 busnum);
-
 /*
  * SPI resource management while processing a SPI message
  */