wl1271: fix the inetdev notifier callback return values

The wl1271_dev_notify() was returning 0 or -ENODEV, when it should return
NOTIFY_* instead.  Now we use NOTIFY_DONE when we didn't handle the event or
NOTIFY_OK when we have handled it.

For inetdev notifications, it doesn't matter whether we use NOTIFY_DONE or
NOTIFY_OK, because it ignores the return value of the call to
blocking_notifier_call_chain().  But the notify.h header says that
NOTIFY_DONE is "Don't care" and NOTIFY_OK is "Suits me", so that seems to be
the right way to do it.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>