[libata] sata_dwc_460ex: signdness bug

dma_dwc_xfer_setup() returns an int and "dma_chan" needs to be signed
for the error handling to work.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_dwc_460ex.c

@@ -1459,7 +1459,7 @@ static void sata_dwc_qc_prep_by_tag(struct ata_queued_cmd *qc, u8 tag)
 {
 	struct scatterlist *sg = qc->sg;
 	struct ata_port *ap = qc->ap;
-	u32 dma_chan;
+	int dma_chan;
 	struct sata_dwc_device *hsdev = HSDEV_FROM_AP(ap);
 	struct sata_dwc_device_port *hsdevp = HSDEVP_FROM_AP(ap);
 	int err;