net/mlx5: fs, call the deletion function of the node

Don't call del_hw_fte() directly, instead use the hardware deletion
function set. This is just a small cleanup and doesn't change anything
as for an FTE the deletion function is already set to del_hw_fte().

Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>