[SCSI] be2iscsi: remove host and session casts

iscsi_session_to_shost is a macro around dev_to_shost which returns a
Scsi_Host so there is no need to cast.

iscsi_session_to_shost is a macro around shost_priv which
returns a void pointer so no need to cast.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>