net/mlx5: Push common deletion code into mlx5_sf_del()

Don't call the same functions for SF deletion on multiple places.
Instead, introduce a helper mlx5_sf_del() and move the code there.

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