A device tree overlay notifier can return NOTIFY_OK, NOTIFY_STOP,
or an embedded errno.  overlay_notify() incorrectly reports an
error for NOTIFY_OK.

Reported-by: atull@kernel.org
Signed-off-by: NFrank Rowand <frank.rowand@sony.com>
Signed-off-by: NRob Herring <robh@kernel.org>