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>

fs/ocfs2/alloc.h

@@ -47,7 +47,7 @@ int ocfs2_remove_extent(struct inode *inode, struct buffer_head *di_bh,
 			struct ocfs2_cached_dealloc_ctxt *dealloc);
 int ocfs2_num_free_extents(struct ocfs2_super *osb,
 			   struct inode *inode,
-			   struct ocfs2_dinode *fe);
+			   struct buffer_head *bh);
 /* how many new metadata chunks would an allocation need at maximum? */
 static inline int ocfs2_extend_meta_needed(struct ocfs2_dinode *fe)
 {