atmel-mci: fix initialization of dma slave data

The conversion of atmel-mci to dma_request_channel missed the
initialization of the channel dma_slave information.  The filter_fn passed
to dma_request_channel is responsible for initializing the channel's
private data.  This implementation has the additional benefit of enabling
a generic client-channel data passing mechanism.

Reviewed-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index a589930..280a9d2 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -518,6 +518,7 @@
 				       dma_chan_name(chan), err);
 			else
 				break;
+			chan->private = NULL;
 			chan = NULL;
 		}
 	}
@@ -536,6 +537,7 @@
 	WARN_ONCE(chan->client_count != 1,
 		  "chan reference count %d != 1\n", chan->client_count);
 	dma_chan_put(chan);
+	chan->private = NULL;
 	mutex_unlock(&dma_list_mutex);
 }
 EXPORT_SYMBOL_GPL(dma_release_channel);