scsi: libfc: fix null pointer dereference on a null lport

Currently if lport is null then the null lport pointer is dereference when
printing out debug via the FC_LPORT_DB macro. Fix this by using the more
generic FC_LIBFC_DBG debug macro instead that does not use lport.

Addresses-Coverity: ("Dereference after null check")
Fixes: 7414705e ("libfc: Add runtime debugging with debug_logging module parameter")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>