dmaengine: s3c24xx-dma: make phy->irq signed for error handling

There is a bug in s3c24xx_dma_probe() where we do:

		phy->irq = platform_get_irq(pdev, i);
		if (phy->irq < 0) {

The problem is that "phy->irq" is unsigned so the error handling doesn't
work.  I have changed it to signed.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>