net/mlx5: fix flow index type
net/mlx5: fix flow index type

Fix assertion check warnings.

Fixes: 8bb81f2649b1 ("net/mlx5: use thread specific flow workspace")
Cc: stable@dpdk.org

Signed-off-by: Xueming Li <a578f76ca98b1dec92e0d1baef814b93f3f2f3b4@nvidia.com>
Reviewed-by: Viacheslav Ovsiienko <5b8db9bb93a9a9aefc8828f79604d1fe963a53dd@nvidia.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk