ion: update API stubs

The stubs for some of the Ion functions have gotten stale since the
last Ion API change. Update these to avoid compile errors when Ion is
not included in the build.

Change-Id: Idfe475c0f1990e5a9b5919434a27ae9dd63ffcb4
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>