TBR: Fix perms.WriteTo in mojo_impl.
TBR: Fix perms.WriteTo in mojo_impl.

Required by v.io/c/14484

Change-Id: Ie382f9580719e676b7454266a413e2d77fb9e8d0

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref