Update `OWNERS` files under `system/security`.

Test: n/a
Change-Id: Ic0e0d868eb715e20f41e14ee5146d54dded2e43b
diff --git a/ondevice-signing/OWNERS b/ondevice-signing/OWNERS
index 72a8eb5..f406fce 100644
--- a/ondevice-signing/OWNERS
+++ b/ondevice-signing/OWNERS
@@ -1,3 +1,3 @@
 maco@google.com
 ngeoffray@google.com
-oth@google.com
+jiakaiz@google.com