scsi_flush_work flushes workqueue for the Scsi_Host.  In iSCSI offload
enabled host, this would wait for all other sessions under the host.

Use flush_work for the session being removed instead.
Signed-off-by: NJitendra Bhivare <jitendra.bhivare@broadcom.com>
Reviewed-by: NTomas Henzl <thenzl@redhat.com>
Reviewed-by: NChris Leech <cleech@redhat.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>