net/mlx5e: Rename representor get devlink port function

Rename representor's mlx5e_get_devlink_port() to
mlx5e_rep_get_devlink_port().
The downstream patch will add a non-representor mlx5e function called
mlx5e_get_devlink_phy_port().

Signed-off-by: Vladyslav Tarasiuk <vladyslavt@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>