switch dentry_open() to struct path, make it grab references itself

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index dde2005..6d38851 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -221,7 +221,7 @@
 extern void selinux_complete_init(void);
 extern int selinux_disable(void);
 extern void exit_sel_fs(void);
-extern struct dentry *selinux_null;
+extern struct path selinux_null;
 extern struct vfsmount *selinuxfs_mount;
 extern void selnl_notify_setenforce(int val);
 extern void selnl_notify_policyload(u32 seqno);