ovl: use i_private only as a key

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 553727d..b8c2138 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -61,6 +61,8 @@
 
 struct ovl_inode {
 	struct inode vfs_inode;
+	struct inode *upper;
+	struct inode *lower;
 };
 
 static inline struct ovl_inode *OVL_I(struct inode *inode)