tcm_fc: Use transport_generic_free_cmd for ft_sess_put in ft_send_tm

transport_generic_free_cmd will end up calling ft_sess_put, so it should
work just the same.

Signed-off-by: Andy Grover <agrover@redhat.com>
Cc: Kiran Patil <kiran.patil@intel.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>