usb: dwc3: Fix incorrect type for utmi mode

The utmi mode is unsigned according the dt-bindings.
Fix sparse issue (-Wtypesign):

  drivers/usb/dwc3/dwc3-omap.c:391:50: warning: incorrect type in argument 3 (different signedness)
  drivers/usb/dwc3/dwc3-omap.c:391:50:    expected unsigned int [usertype] *out_value
  drivers/usb/dwc3/dwc3-omap.c:391:50:    got int *<noident>
Signed-off-by: Franck Demathieu <fdemathieu@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/dwc3-omap.c

@@ -392,7 +392,7 @@ static void dwc3_omap_set_utmi_mode(struct dwc3_omap *omap)
 {
 	u32			reg;
 	struct device_node	*node = omap->dev->of_node;
-	int			utmi_mode = 0;
+	u32			utmi_mode = 0;
 
 	reg = dwc3_omap_read_utmi_ctrl(omap);