overlay: Search for right debugfs path

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/overlay/debugfs.h b/overlay/debugfs.h
index 476553c..0e5ad95 100644
--- a/overlay/debugfs.h
+++ b/overlay/debugfs.h
@@ -25,6 +25,7 @@
 #ifndef DEBUGFS_H
 #define DEBUGFS_H
 
+extern char debugfs_path[128];
 int debugfs_init(void);
 
 #endif /* DEBUGFS_H */