kill f_dentry macro

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index b6b55a9..fa2db08 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -467,3 +467,7 @@
 [mandatory]
 	d_materialise_unique() is gone; d_splice_alias() does everything you
 	need now.  Remember that they have opposite orders of arguments ;-/
+--
+[mandatory]
+	f_dentry is gone; use f_path.dentry, or, better yet, see if you can avoid
+	it entirely.