zfcp: restore: Dont use 0 to indicate invalid LUN in rec trace

bring back
commit d21e9daa
("[SCSI] zfcp: Dont use 0 to indicate invalid LUN in rec trace")
which was lost with
commit ae0904f6


("[SCSI] zfcp: Redesign of the debug tracing for recovery actions.")

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Fixes: ae0904f6

 ("[SCSI] zfcp: Redesign of the debug tracing for recovery actions.")
Cc: <stable@vger.kernel.org> #2.6.38+
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>