scsi: core: Remove struct scsi_pointer from struct scsi_cmnd

Remove struct scsi_pointer from struct scsi_cmnd since the previous patches
removed all users of that member of struct scsi_cmnd. Additionally, reorder
the members of struct scsi_cmnd such that the statement that the field
below can be modified by the SCSI LLD is again correct.

Link: https://lore.kernel.org/r/20220218195117.25689-50-bvanassche@acm.org


Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>