fsnotify: Allocate overflow events with proper type

Commit 7053aee26a35 "fsnotify: do not share events between notification
groups" used overflow event statically allocated in a group with the
size of the generic notification event. This causes problems because
some code looks at type specific parts of event structure and gets
confused by a random data it sees there and causes crashes.

Fix the problem by allocating overflow event with type corresponding to
the group type so code cannot get confused.

Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index c84bc7c..64cf3ef 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -160,7 +160,7 @@
 
 	struct fasync_struct *fsn_fa;    /* async notification */
 
-	struct fsnotify_event overflow_event;	/* Event we queue when the
+	struct fsnotify_event *overflow_event;	/* Event we queue when the
 						 * notification list is too
 						 * full */