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>

drivers/dma/at_xdmac.c

@@ -1333,7 +1333,7 @@ at_xdmac_prep_dma_memset_sg(struct dma_chan *chan, struct scatterlist *sgl,
 		 * 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);