[SCSI] iscsi_transport, qla4xxx: have class lookup host for drivers

We are going to be adding more host level sysfs attrs and
set_params, so this patch has them take a scsi_host instead
of either a scsi_host or host no.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Cc: David C Somayajulu <david.somayajulu@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>