net/mlx5e: Only skip encap flows update when encap init failed

When encap entry initialization completes successfully e->compl_result is
set to positive value and not zero, like mlx5e_rep_update_flows() assumes
at the moment. Fix the conditional to only skip encap flows update when
e->compl_result < 0.

Fixes: 2a1f1768 ("net/mlx5e: Refactor neigh update for concurrent execution")
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>