Revert "dmaengine: Add a warning for drivers not using the generic slave caps retrieval"

This reverts commit ecc19d17.

It added a new warning to try to encourage driver writers to set the
device capabities properly, but drivers haven't been updated and in the
meantime it just generaters a scary message that users cannot actually
do anything about.

Warnings like these are appropriate if you actually expect to fix the
code that causes them.  They are not appropriate for releases.
Requested-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/dma/dmaengine.c

@@ -859,9 +859,6 @@ int dma_async_device_register(struct dma_device *device)
 	BUG_ON(!device->device_issue_pending);
 	BUG_ON(!device->dev);
 
-	WARN(dma_has_cap(DMA_SLAVE, device->cap_mask) && !device->directions,
-	     "this driver doesn't support generic slave capabilities reporting\n");
-
 	/* note: this only matters in the
 	 * CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH=n case
 	 */