procfs: new helper - PDE_DATA(inode)

The only part of proc_dir_entry the code outside of fs/proc
really cares about is PDE(inode)->data.  Provide a helper
for that; static inline for now, eventually will be moved
to fs/proc, along with the knowledge of struct proc_dir_entry
layout.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 3863b8f..537301a 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2714,7 +2714,7 @@
 
 	if (!ret) {
 		struct seq_file *sf = file->private_data;
-		sf->private = PDE(inode)->data;
+		sf->private = PDE_DATA(inode);
 	}
 	return ret;
 };