dmaengine: initialize tx_list in dma_async_tx_descriptor_init

Centralize this common initialization (and one case where ipu_idmac is
duplicating ->chan initialization).

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/dmaengine.c

@@ -920,6 +920,7 @@ void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx,
 {
 	tx->chan = chan;
 	spin_lock_init(&tx->lock);
+	INIT_LIST_HEAD(&tx->tx_list);
 }
 EXPORT_SYMBOL(dma_async_tx_descriptor_init);