usb: host: xhci-omap: fix build break

Fix the following build break:

drivers/usb/host/xhci-omap.c:35:5: error: ‘board_usb_init’ aliased to external symbol ‘__board_usb_init’
 int board_usb_init(int index, enum usb_init_type init)
      ^

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/host/xhci-omap.c

@@ -27,7 +27,7 @@ DECLARE_GLOBAL_DATA_PTR;
 
 static struct omap_xhci omap;
 
-inline int __board_usb_init(int index, enum usb_init_type init)
+__weak int __board_usb_init(int index, enum usb_init_type init)
 {
 	return 0;
 }