Btrfs: rename

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index da12d82..3330004 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -32,6 +32,7 @@
 #define BTRFS_CSUM_SIZE 32
 /* four bytes for CRC32 */
 #define BTRFS_CRC32_SIZE 4
+#define BTRFS_EMPTY_DIR_SIZE 6
 
 /*
  * the key defines the order in the tree, and so it also defines (optimal)