Which would result in NPE after when userspace connected again.

Expired command would be freed either when handling command(by userspace),
or when device was tearing down
Reviewed-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Sheng Yang <sheng@yasker.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>