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

This reverts commit ecc19d17868be9c9f8f00ed928791533c420f3e0.

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 <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/dma/dmaengine.c

···
 	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
 	 */