ib_srp: Remove WARN_ON in srp_terminate_io()

The WARN_ON() is pointless as the rport is placed in SDEV_TRANSPORT_OFFLINE
at that time, so no new commands can be submitted via srp_queuecommand()

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.com>
Acked-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>