net/mlx5: unlock on error path in esw_vfs_changed_event_handler()

Unlock before returning on this error path.

Fixes: f1bc646c ("net/mlx5: Use devl_ API in mlx5_esw_offloads_devlink_port_register")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>