dw_dmac: introduce to_dw_desc() macro

The to_dw_desc() macro helps to retrieve the dw_desc node from the
corresponding list_head structure.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>
diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
index 9a27fb7..476e9c8 100644
--- a/drivers/dma/dw_dmac.c
+++ b/drivers/dma/dw_dmac.c
@@ -93,7 +93,7 @@
 
 static struct dw_desc *dwc_first_active(struct dw_dma_chan *dwc)
 {
-	return list_entry(dwc->active_list.next, struct dw_desc, desc_node);
+	return to_dw_desc(dwc->active_list.next);
 }
 
 static struct dw_desc *dwc_desc_get(struct dw_dma_chan *dwc)
@@ -600,9 +600,7 @@
 			if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
 				if (dwc->tx_node_active != dwc->tx_list) {
 					struct dw_desc *desc =
-						list_entry(dwc->tx_node_active,
-							   struct dw_desc,
-							   desc_node);
+						to_dw_desc(dwc->tx_node_active);
 
 					dma_writel(dw, CLEAR.XFER, dwc->mask);