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>

drivers/scsi/libfc/fc_exch.c

@@ -2591,7 +2591,7 @@ void fc_exch_recv(struct fc_lport *lport, struct fc_frame *fp)
 
 	/* lport lock ? */
 	if (!lport || lport->state == LPORT_ST_DISABLED) {
-		FC_LPORT_DBG(lport, "Receiving frames for an lport that "
+		FC_LIBFC_DBG("Receiving frames for an lport that "
 			     "has not been initialized correctly\n");
 		fc_frame_free(fp);
 		return;