dmaengine: at_xdmac: fix false condition for memset_sg transfers

The code was not in agreement with the comments.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Cc: stable@vger.kernel.org # 4.3 and later
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index d09277f..c344f89 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -1333,7 +1333,7 @@
 		 * since we don't care about the stride anymore.
 		 */
 		if ((i == (sg_len - 1)) &&
-		    sg_dma_len(ppsg) == sg_dma_len(psg)) {
+		    sg_dma_len(psg) == sg_dma_len(sg)) {
 			dev_dbg(chan2dev(chan),
 				"%s: desc 0x%p can be merged with desc 0x%p\n",
 				__func__, desc, pdesc);