[SCSI] imm: convert to accessors and !use_sg cleanup

 - convert to accessors and !use_sg cleanup
 - Not ready for sg-chaining

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Tested-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>