scsi: scsi_debug: Constify sdebug_driver_template

It's better to have sdebug_driver_template as const, so update the probe
path to set the shost members directly after allocation and make that
change.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20250107153325.1689432-1-john.g.garry@oracle.com


Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>