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>

include/linux/proc_fs.h

@@ -306,6 +306,11 @@ static inline struct proc_dir_entry *PDE(const struct inode *inode)
 	return PROC_I(inode)->pde;
 }
 
+static inline void *PDE_DATA(const struct inode *inode)
+{
+	return PROC_I(inode)->pde->data;
+}
+
 static inline struct net *PDE_NET(struct proc_dir_entry *pde)
 {
 	return pde->parent->data;