scsi: core: Declare most SCSI host template pointers const

Prepare for constifying most SCSI host template pointers by constifying the
SCSI host template pointer arguments and variables in the SCSI core.

Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20230322195515.1267197-3-bvanassche@acm.org


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>