libpayload: Clean up USB build warnings

There were a few build warnings in the USB driver to clean
up before -Werror may be enabled.

Change-Id: I220cfcf0ee926912a184a91d3ced3ba61259130e
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-on: http://review.coreboot.org/7921
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

payloads/libpayload/drivers/usb/usbinit.c

@@ -172,15 +172,15 @@ hci_t *usb_add_mmio_hc(hc_type type, void *bar)
 	switch (type) {
 #ifdef CONFIG_LP_USB_OHCI
 	case OHCI:
-		return ohci_init(bar);
+		return ohci_init((unsigned long)bar);
 #endif
 #ifdef CONFIG_LP_USB_EHCI
 	case EHCI:
-		return ehci_init(bar);
+		return ehci_init((unsigned long)bar);
 #endif
 #ifdef CONFIG_LP_USB_XHCI
 	case XHCI:
-		return xhci_init(bar);
+		return xhci_init((unsigned long)bar);
 #endif
 	default:
 		usb_debug("HC type %d (at %p) is not supported!\n", type, bar);