fsnotify: Do not return merged event from fsnotify_add_notify_event()

The event returned from fsnotify_add_notify_event() cannot ever be used
safely as the event may be freed by the time the function returns (after
dropping notification_mutex). So change the prototype to just return
whether the event was added or merged into some existing event.

Reported-and-tested-by: Jiri Kosina <jkosina@suse.cz>
Reported-and-tested-by: Dave Jones <davej@fedoraproject.org>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --cc fs/notify/fanotify/fanotify.c
Simple merge

diff --cc fs/notify/inotify/inotify_fsnotify.c
Simple merge

diff --cc fs/notify/notification.c
Simple merge

diff --cc include/linux/fsnotify_backend.h
Simple merge