inotify: drop user watch count when a watch is removed

The inotify rewrite forgot to drop the inotify watch use cound when a watch
was removed.  This means that a single inotify fd can only ever register a
maximum of /proc/sys/fs/max_user_watches even if some of those had been
freed.

Signed-off-by: Eric Paris <eparis@redhat.com>

fs/notify/inotify/inotify_user.c

@@ -404,6 +404,8 @@ skip_send_ignore:
 
 	/* removed from idr, drop that reference */
 	fsnotify_put_mark(entry);
+
+	atomic_dec(&group->inotify_data.user->inotify_watches);
 }
 
 /* ding dong the mark is dead */