dmaengine: fix memleak in dma_async_device_unregister

While debugging a dma driver I noticed a memleak after
unloading the driver module.

Caught by kmemleak.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/dmaengine.c

@@ -826,6 +826,7 @@ void dma_async_device_unregister(struct dma_device *device)
 		chan->dev->chan = NULL;
 		mutex_unlock(&dma_list_mutex);
 		device_unregister(&chan->dev->device);
+		free_percpu(chan->local);
 	}
 }
 EXPORT_SYMBOL(dma_async_device_unregister);