procfs: switch /proc/self away from proc_dir_entry

Just have it pinned in dcache all along and let procfs ->kill_sb()
drop it before kill_anon_super().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/proc/root.c b/fs/proc/root.c
index c6e9fac..20834b3 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -137,6 +137,8 @@
 	struct pid_namespace *ns;
 
 	ns = (struct pid_namespace *)sb->s_fs_info;
+	if (ns->proc_self)
+		dput(ns->proc_self);
 	kill_anon_super(sb);
 	put_pid_ns(ns);
 }