In case handle_eth_ud_smac_index fails, we need to free the allocated resources.

Fixes: 2f5bb473 ("mlx4: Add ref counting to port MAC table for RoCE")
Signed-off-by: NMajd Dibbiny <majd@mellanox.com>
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NRoland Dreier <roland@purestorage.com>