dmaengine: provide a common function for completing a dma descriptor

Provide a common function to do the cookie mechanics for completing
a DMA descriptor.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jassi Brar <jassisinghbrar@gmail.com>
[imx-sdma.c & mxs-dma.c]
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>

drivers/dma/intel_mid_dma.c

@@ -290,7 +290,7 @@ static void midc_descriptor_complete(struct intel_mid_dma_chan *midc,
 	struct intel_mid_dma_lli	*llitem;
 	void *param_txd = NULL;
 
-	midc->chan.completed_cookie = txd->cookie;
+	dma_cookie_complete(txd);
 	callback_txd = txd->callback;
 	param_txd = txd->callback_param;