USB: Add EXPORT_SYMBOL for usb_alloc_dev

usb_alloc_dev is used by lvstest driver now which can be built as
module. Therefore export usb_alloc_dev symbol.
Signed-off-by: NPratyush Anand <pratyush.anand@st.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/usb.c

@@ -501,6 +501,7 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
 	}
 	return dev;
 }
+EXPORT_SYMBOL_GPL(usb_alloc_dev);
 
 /**
  * usb_get_dev - increments the reference count of the usb device structure