wcn36xx: don't process 'valid' descriptors

The DMA engine will reset the valid bit after a descriptor is
complete; any with the valid bit still set may still be in
use by the hardware, so check that before freeing the descriptor.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
diff --git a/drivers/net/wireless/ath/wcn36xx/dxe.c b/drivers/net/wireless/ath/wcn36xx/dxe.c
index 73f12f1..3d6bc9b 100644
--- a/drivers/net/wireless/ath/wcn36xx/dxe.c
+++ b/drivers/net/wireless/ath/wcn36xx/dxe.c
@@ -354,6 +354,8 @@
 	 * and while-do will not make any cycles.
 	 */
 	do {
+		if (ctl->desc->ctrl & WCN36XX_DXE_CTRL_VALID_MASK)
+			break;
 		if (ctl->skb) {
 			dma_unmap_single(NULL, ctl->desc->src_addr_l,
 					 ctl->skb->len, DMA_TO_DEVICE);