USB: wusbcore/wa-xfer, fix lock imbalance

Fix locking on one wa_urb_enqueue_b's fail path. There was omitted unlock.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/wusbcore/wa-xfer.c

@@ -921,8 +921,10 @@ static void wa_urb_enqueue_b(struct wa_xfer *xfer)
 	result = -ENODEV;
 	/* FIXME: segmentation broken -- kills DWA */
 	mutex_lock(&wusbhc->mutex);		/* get a WUSB dev */
-	if (urb->dev == NULL)
+	if (urb->dev == NULL) {
+		mutex_unlock(&wusbhc->mutex);
 		goto error_dev_gone;
+	}
 	wusb_dev = __wusb_dev_get_by_usb_dev(wusbhc, urb->dev);
 	if (wusb_dev == NULL) {
 		mutex_unlock(&wusbhc->mutex);