net/mlx5e: Always set attr mdev pointer

Eswitch offloads extensions in following patches in the series require
attr->esw_attr->in_mdev pointer to always be set. This is already the case
for all code paths except mlx5_tc_ct_entry_add_rule() function. Fix the
function to assign mdev pointer with priv->mdev value.

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>