scsi: tracing: Fix handling of TRANSFER LENGTH == 0 for READ(6) and WRITE(6)

scsi: tracing: Fix handling of TRANSFER LENGTH == 0 for READ(6) and WRITE(6)

According to SBC-2 a TRANSFER LENGTH field of zero means that 256 logical
blocks must be transferred. Make the SCSI tracing code follow SBC-2.

Fixes: bf8162354233 ("[SCSI] add scsi trace core functions and put trace points")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Link: https://lore.kernel.org/r/20191105215553.185018-1-bvanassche@acm.org
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>