net/mlx5: E-switch, Avoid extack error log for disabled vport

When E-switch vport is disabled, querying its hardware address is
unsupported.
Avoid setting extack error log message in such case.

Fixes: f099fde1 ("net/mlx5: E-switch, Support querying port function mac address")
Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>