net/mlx5: fix return value of start operation

On error, mlx5_dev_start() does not return a negative value
as it is supposed to do. The consequence is that the application
(ex: testpmd) does not notice that the port is not started
and begins the rxtx on an uninitialized port, which crashes.

Fixes: e1016cb73383 ("net/mlx5: fix Rx interrupts management")
Cc: stable@dpdk.org

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>

drivers/net/mlx5/mlx5_trigger.c

@@ -181,7 +181,7 @@ error:
 	priv_rxq_stop(priv);
 	priv_flow_delete_drop_queue(priv);
 	priv_unlock(priv);
-	return -err;
+	return err;
 }
 
 /**