dnotify: replace dnotify_mark_mutex with mark mutex of dnotify_group

dnotify: replace dnotify_mark_mutex with mark mutex of dnotify_group

There is no need to use a special mutex to protect against the fcntl/close
race (see dnotify.c for a description of this race).  Instead the
dnotify_groups mark mutex can be used.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: Eric Paris <eparis@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>