scsi: target: core: Move t_task_cdb initialization

scsi: target: core: Move t_task_cdb initialization

Prepare to split target_submit_cmd_map_sgls() so the initialization and
submission part can be called at different times. If the init part fails we
can reference the t_task_cdb early in some of the logging and tracing
code. Move it to transport_init_se_cmd() so we don't hit NULL pointer
crashes.

Link: https://lore.kernel.org/r/20210227170006.5077-2-michael.christie@oracle.com
Tested-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>