net/mlx5: Remove SF table reference counting

Historically, the SF table reference counting was present in order to
protect parallel executions of devlink ops. However, since currently
this is protected with devlink instance lock, the SF table reference
counting is no longer needed. Remove it entirely.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>