usb: gadget: fix g_serial regression

Commit "usb: gadget: use config_ep_by_speed() instead of
ep_choose()" broke g_serial in "non ACM nor OBEX"
mode. Apply a trivial fix on usb endpoints discovery.
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/f_serial.c

@@ -131,8 +131,8 @@ static int gser_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
 	}
 	if (!gser->port.in->desc || !gser->port.out->desc) {
 		DBG(cdev, "activate generic ttyGS%d\n", gser->port_num);
-		if (!config_ep_by_speed(cdev->gadget, f, gser->port.in) ||
-		    !config_ep_by_speed(cdev->gadget, f, gser->port.out)) {
+		if (config_ep_by_speed(cdev->gadget, f, gser->port.in) ||
+		    config_ep_by_speed(cdev->gadget, f, gser->port.out)) {
 			gser->port.in->desc = NULL;
 			gser->port.out->desc = NULL;
 			return -EINVAL;