dmaengine: at_hdmac: fix device leak on of_dma_xlate()

Make sure to drop the reference taken when looking up the DMA platform
device during of_dma_xlate() when releasing channel resources.

Note that commit 3832b78b3ec2 ("dmaengine: at_hdmac: add missing
put_device() call in at_dma_xlate()") fixed the leak in a couple of
error paths but the reference is still leaking on successful allocation.

Fixes: bbe89c8e3d59 ("at_hdmac: move to generic DMA binding")
Fixes: 3832b78b3ec2 ("dmaengine: at_hdmac: add missing put_device() call in at_dma_xlate()")
Cc: [e-mail] # 3.10: 3832b78b3ec2
Cc: Yu Kuai <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/at_hdmac.c

···
 static void atc_free_chan_resources(struct dma_chan *chan)
 {
 	struct at_dma_chan	*atchan = to_at_dma_chan(chan);
+	struct at_dma_slave	*atslave;
 
 	BUG_ON(atc_chan_is_enabled(atchan));
 
···
 	/*
 	 * Free atslave allocated in at_dma_xlate()
 	 */
-	kfree(chan->private);
-	chan->private = NULL;
+	atslave = chan->private;
+	if (atslave) {
+		put_device(atslave->dma_dev);
+		kfree(atslave);
+		chan->private = NULL;
+	}
 
 	dev_vdbg(chan2dev(chan), "free_chan_resources: done\n");
 }