of: overlay: do not break notify on NOTIFY_{OK|STOP}

We should not break overlay notifications on NOTIFY_{OK|STOP}
otherwise we might break on the first fragment. We should only stop
notifications if a *real* errno is returned by one of the listeners.

Fixes: a1d19bd4 ("of: overlay: pr_err from return NOTIFY_OK to overlay apply/remove")
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220420130205.89435-1-nuno.sa@analog.com