dmaengine: mxs-dma: skip request_irq for NO_IRQ

In general, the mxs-dma users get separate irq for each channel,
but gpmi is special one which has only one irq shared by all gpmi
channels.  It causes mxs_dma channel allocation function fail for
all other gpmi channels except the first one calling into the
function.

The patch gets request_irq call skipped for NO_IRQ case, and leaves
this gpmi specific quirk to gpmi driver to sort out.  It will fix
above problem if gpmi driver sets chan_irq as gpmi irq for only one
channel and NO_IRQ for all the rest channels.
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>
Cc: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

drivers/dma/mxs-dma.c

@@ -327,10 +327,12 @@ static int mxs_dma_alloc_chan_resources(struct dma_chan *chan)
 
 	memset(mxs_chan->ccw, 0, PAGE_SIZE);
 
-	ret = request_irq(mxs_chan->chan_irq, mxs_dma_int_handler,
-				0, "mxs-dma", mxs_dma);
-	if (ret)
-		goto err_irq;
+	if (mxs_chan->chan_irq != NO_IRQ) {
+		ret = request_irq(mxs_chan->chan_irq, mxs_dma_int_handler,
+					0, "mxs-dma", mxs_dma);
+		if (ret)
+			goto err_irq;
+	}
 
 	ret = clk_enable(mxs_dma->clk);
 	if (ret)