dmaengine: shdma: remove legacy slave_id parsing

The slave device is picked through either devicetree or a filter
function, and any remaining out-of-tree drivers would have warned
about this usage since 2015.

Stop interpreting the field finally so it can be removed from
the interface.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211122222203.4103644-6-arnd@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/sh/shdma-base.c

@@ -786,14 +786,6 @@ static int shdma_config(struct dma_chan *chan,
 	if (!config)
 		return -EINVAL;
 
-	/*
-	 * overriding the slave_id through dma_slave_config is deprecated,
-	 * but possibly some out-of-tree drivers still do it.
-	 */
-	if (WARN_ON_ONCE(config->slave_id &&
-			 config->slave_id != schan->real_slave_id))
-		schan->real_slave_id = config->slave_id;
-
 	/*
 	 * We could lock this, but you shouldn't be configuring the
 	 * channel, while using it...