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/fs/jbd2/journal.c b/fs/jbd2/journal.c
index ed10991..154592e 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -950,7 +950,7 @@
 
 static int jbd2_seq_info_open(struct inode *inode, struct file *file)
 {
-	journal_t *journal = PDE(inode)->data;
+	journal_t *journal = PDE_DATA(inode);
 	struct jbd2_stats_proc_session *s;
 	int rc, size;