dmaengine: stm32-dma: Fix unsigned variable compared with zero

Commit f4fd2ec0: ("dmaengine: stm32-dma: use platform_get_irq()") used
unsigned variable irq to store the results and check later for negative
errors, so update the code to use signed variable for this

Fixes: f4fd2ec0 ("dmaengine: stm32-dma: use platform_get_irq()")
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@lip6.fr>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/stm32-dma.c

@@ -1303,13 +1303,15 @@ static int stm32_dma_probe(struct platform_device *pdev)
 	for (i = 0; i < STM32_DMA_MAX_CHANNELS; i++) {
 		chan = &dmadev->chan[i];
 		chan->irq = platform_get_irq(pdev, i);
-		if (chan->irq < 0)  {
-			ret = chan->irq;
+		ret = platform_get_irq(pdev, i);
+		if (ret < 0)  {
 			if (ret != -EPROBE_DEFER)
 				dev_err(&pdev->dev,
 					"No irq resource for chan %d\n", i);
 			goto err_unregister;
 		}
+		chan->irq = ret;
+
 		ret = devm_request_irq(&pdev->dev, chan->irq,
 				       stm32_dma_chan_irq, 0,
 				       dev_name(chan2dev(chan)), chan);