IB/iser: Remove a redundant always-false condition

We always call iser_initialize_task_headers() and set
the header tx_sg.lkey to the device mr lkey, so no
point in checking it in iser_create_send_desc().

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>