usb: gadget: udc: at91: use PTR_ERR_OR_ZERO()

coccicheck found this pattern which could be
converted to PTR_ERR_OR_ZERO(). No functional
changes.

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
diff --git a/drivers/usb/gadget/udc/at91_udc.c b/drivers/usb/gadget/udc/at91_udc.c
index d0d1894..8bc7841 100644
--- a/drivers/usb/gadget/udc/at91_udc.c
+++ b/drivers/usb/gadget/udc/at91_udc.c
@@ -1726,10 +1726,7 @@
 
 	udc->matrix = syscon_regmap_lookup_by_phandle(udc->pdev->dev.of_node,
 						      "atmel,matrix");
-	if (IS_ERR(udc->matrix))
-		return PTR_ERR(udc->matrix);
-
-	return 0;
+	return PTR_ERR_OR_ZERO(udc->matrix);
 }
 
 static void at91sam9261_udc_pullup(struct at91_udc *udc, int is_on)