scsi: ia64: simscsi: use request tag instead of serial_number

Use the request tag for logging instead of the scsi command serial
number.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[jejb: fix commit oneliner]
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>