net/mlx4_en: fix off by one in error handling

If an error occurs in mlx4_init_eq_table the index used in the
err_out_unmap label is one too big which results in a panic in
mlx4_free_eq. This patch fixes the index in the error path.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>