dmaengine: core: Revert back to pr_debug in __dma_request_channel()

Commit ef859312c3a1 ("dmaengine: core: Use dev_ functions for debug and
error prints") wasn't quite right in __dma_request_channel() by claiming
that all pr_ prints have valid DMA channel pointer. Obviously it is not
true as __dma_request_channel() is looking for a channel and returns NULL
if it does not find it.

Prevent this potential NULL pointer dereference by reverting back to
pr_debug().

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/dmaengine.c

@@ -664,7 +664,7 @@ struct dma_chan *__dma_request_channel(const dma_cap_mask_t *mask,
 	}
 	mutex_unlock(&dma_list_mutex);
 
-	dev_dbg(chan->device->dev, "%s: %s (%s)\n",
+	pr_debug("%s: %s (%s)\n",
 		 __func__,
 		 chan ? "success" : "fail",
 		 chan ? dma_chan_name(chan) : NULL);