at_hdmac: implement a private tx_list

Drop at_hdmac's use of tx_list from struct dma_async_tx_descriptor in
preparation for removal of this field.

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>


diff --git a/drivers/dma/at_hdmac_regs.h b/drivers/dma/at_hdmac_regs.h
index 4c972af..495457e 100644
--- a/drivers/dma/at_hdmac_regs.h
+++ b/drivers/dma/at_hdmac_regs.h
@@ -165,6 +165,7 @@
 	struct at_lli			lli;
 
 	/* THEN values for driver housekeeping */
+	struct list_head		tx_list;
 	struct dma_async_tx_descriptor	txd;
 	struct list_head		desc_node;
 	size_t				len;