nvmet-tcp: always initialize tls_handshake_tmo_work

The TLS handshake timeout work item should always be
initialized to avoid a crash when cancelling the workqueue.

Fixes: 675b453e

 ("nvmet-tcp: enable TLS handshake upcall")
Suggested-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>