usb: renesas_usbhs: gadget: remove extra check on udc_stop

usb_gadget_ops :: udc_stop might be called with driver = NULL since
511f3c5326eabe1ece35202a404c24c0aeacc246
(usb: gadget: udc-core: fix a regression during gadget driver unbinding)

Because of that, 2nd times insmod goes fail.
This patch fixes it up.

Reported-by: Yusuke Goda <[e-mail]>
Signed-off-by: Kuninori Morimoto <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/renesas_usbhs/mod_gadget.c

···
 	struct usbhsg_gpriv *gpriv = usbhsg_gadget_to_gpriv(gadget);
 	struct usbhs_priv *priv = usbhsg_gpriv_to_priv(gpriv);
 
-	if (!driver		||
-	    !driver->unbind)
-		return -EINVAL;
-
 	usbhsg_try_stop(priv, USBHSG_STATUS_REGISTERD);
 	gpriv->driver = NULL;