dmaengine: coh901318: Only calculate residue if txstate exists.

There is no point in calculating the residue if there is no
txstate to store the value.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
diff --git a/drivers/dma/coh901318.c b/drivers/dma/coh901318.c
index c340ca9..c100616 100644
--- a/drivers/dma/coh901318.c
+++ b/drivers/dma/coh901318.c
@@ -2422,7 +2422,7 @@
 	enum dma_status ret;
 
 	ret = dma_cookie_status(chan, cookie, txstate);
-	if (ret == DMA_COMPLETE)
+	if (ret == DMA_COMPLETE || !txstate)
 		return ret;
 
 	dma_set_residue(txstate, coh901318_get_bytes_left(chan));