ovl: permission: return ECHILD instead of ENOENT

The error is due to RCU and is temporary.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 041db9c..0598c16 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -128,7 +128,7 @@
 	realinode = d_inode_rcu(realdentry);
 	if (!realinode) {
 		WARN_ON(!(mask & MAY_NOT_BLOCK));
-		return -ENOENT;
+		return -ECHILD;
 	}
 
 	/*