scsi_debug: make jiffy delay name clearer

Add 'j' to delay names to make it clearer that its unit is jiffies and
to differentiate it from sdebug_ndelay whose unit is nanoseconds.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Hannes Reinicke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>