IB/core: Fix unused variable warning

Fix the below "make W=1" build warning:

    drivers/infiniband/core/iwcm.c: In function ‘destroy_cm_id’:
    drivers/infiniband/core/iwcm.c:330: warning: variable ‘ret’ set but not used
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NRoland Dreier <roland@purestorage.com>

drivers/infiniband/core/iwcm.c

@@ -334,7 +334,6 @@ static void destroy_cm_id(struct iw_cm_id *cm_id)
 {
 	struct iwcm_id_private *cm_id_priv;
 	unsigned long flags;
-	int ret;
 
 	cm_id_priv = container_of(cm_id, struct iwcm_id_private, id);
 	/*
@@ -350,7 +349,7 @@ static void destroy_cm_id(struct iw_cm_id *cm_id)
 		cm_id_priv->state = IW_CM_STATE_DESTROYING;
 		spin_unlock_irqrestore(&cm_id_priv->lock, flags);
 		/* destroy the listening endpoint */
-		ret = cm_id->device->iwcm->destroy_listen(cm_id);
+		cm_id->device->iwcm->destroy_listen(cm_id);
 		spin_lock_irqsave(&cm_id_priv->lock, flags);
 		break;
 	case IW_CM_STATE_ESTABLISHED: