ocfs2: Modify ocfs2_num_free_extents for future xattr usage.

ocfs2_num_free_extents() is used to find the number of free extent records
in an inode btree. Hence, it takes an "ocfs2_dinode" parameter. We want to
use this for extended attribute trees in the future, so genericize the
interface the take a buffer head. A future patch will allow that buffer_head
to contain any structure rooting an ocfs2 btree.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 29ff57e..377acb2 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -368,12 +368,13 @@
  */
 int ocfs2_num_free_extents(struct ocfs2_super *osb,
 			   struct inode *inode,
-			   struct ocfs2_dinode *fe)
+			   struct buffer_head *bh)
 {
 	int retval;
 	struct ocfs2_extent_list *el;
 	struct ocfs2_extent_block *eb;
 	struct buffer_head *eb_bh = NULL;
+	struct ocfs2_dinode *fe = (struct ocfs2_dinode *)bh->b_data;
 
 	mlog_entry_void();