scsi: export 'wwid' to sysfs

Use scsi_vpd_lun_id() to export the world-wide unique id (wwid) to
sysfs.  Note that this is the 'best' wwid according to the rules in
scsi_vpd_lun_id(), not every possible wwid presented by the drive.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>