Man page 9 : usb_register_driver

usb_register_driver - register a USB interface driver

int usb_register_driver(struct usb_driver *  new_driver , struct module *  owner , const char *  mod_name );

new_driver
    USB operations for the interface driver

owner
    module owner of this driver.

mod_name
    module name string

Registers a USB interface driver with the USB core. The list of unattached interfaces will be rescanned whenever a new driver is added, allowing the new driver to attach to any recognized interfaces. Returns a negative error code on failure and 0 on success.

if you want your driver to use the USB major number, you must call usb_register_dev to enable that functionality. This function no longer takes care of that.