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>

fs/ext4/mballoc.c

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index ee6614bd..28e421c 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2149,7 +2149,7 @@
 
 static int ext4_mb_seq_groups_open(struct inode *inode, struct file *file)
 {
-	struct super_block *sb = PDE(inode)->data;
+	struct super_block *sb = PDE_DATA(inode);
 	int rc;
 
 	rc = seq_open(file, &ext4_mb_seq_groups_ops);