[SCSI] iscsi bugfixes: fix oops when removing session

We are touching the cls_session after we have freed
it. This causes a oops.

Signed-off-by: Or Gerlitz <ogerlitz@voltaire.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>