usb gadget: fix fsl_usb2_udc potential OOPS

For fsl_usb2_udc driver, ep0 also has a descriptor.  Current code is
misleading and contains a logical mistake.  Here is the patch to fix it.

 http://bugzilla.kernel.org/show_bug.cgi?id=9595

Cc: stable <stable@kernel.org>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/fsl_usb2_udc.c

@@ -776,7 +776,7 @@ fsl_ep_queue(struct usb_ep *_ep, struct usb_request *_req, gfp_t gfp_flags)
 		VDBG("%s, bad params\n", __FUNCTION__);
 		return -EINVAL;
 	}
-	if (!_ep || (!ep->desc && ep_index(ep))) {
+	if (unlikely(!_ep || !ep->desc)) {
 		VDBG("%s, bad ep\n", __FUNCTION__);
 		return -EINVAL;
 	}