sata_mv: silence an uninitialized variable warning

Gcc version 4.6.2-12 complains that if we can't find the "nr-ports"
property in of_property_read_u32_array() then "n_ports" is used
uninitialized.  Let's set it to zero in that case.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_mv.c

@@ -4025,7 +4025,8 @@ static int mv_platform_probe(struct platform_device *pdev)
 	struct ata_host *host;
 	struct mv_host_priv *hpriv;
 	struct resource *res;
-	int n_ports, rc;
+	int n_ports = 0;
+	int rc;
 
 	ata_print_version_once(&pdev->dev, DRV_VERSION);