Clean up the code that checks the validity of a USB gadget driver
in usb_gadget_register_driver(). Moreover, limit the speed of the
driver to either FULL or HIGH, this is more precise and once we
have xHCI support, also more correct.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Lei Wen <leiwen@marvell.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Stefano Babic <sbabic@denx.de>
        struct mv_udc *udc;
        int ret;
 
-       if (!driver
-                       || driver->speed < USB_SPEED_FULL
-                       || !driver->bind
-                       || !driver->setup) {
-               DBG("bad parameter.\n");
+       if (!driver)
+               return -EINVAL;
+       if (!driver->bind || !driver->setup || !driver->disconnect)
+               return -EINVAL;
+       if (driver->speed != USB_SPEED_FULL && driver->speed != USB_SPEED_HIGH)
                return -EINVAL;
-       }
 
        ret = usb_lowlevel_init(0, (void **)&controller.ctrl);
        if (ret)