scsi: qla2xxx: Constify struct qla_tgt_func_tmpl

scsi: qla2xxx: Constify struct qla_tgt_func_tmpl

Since the target function pointers are not modified at runtime, declare the
data structure with the target function pointers const.

Link: https://lore.kernel.org/r/20210320232359.941-3-bvanassche@acm.org
Cc: Quinn Tran <qutran@marvell.com>
Cc: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>