[GFS2] Remove gfs2_databuf in favour of gfs2_bufdata structure

Removing the gfs2_databuf structure and using gfs2_bufdata instead
is a step towards allowing journaling of data without requiring the
metadata header on each journaled block. The idea is to merge the
code paths for ordered data with that of journaled data, with the
log operations in lops.c tacking account of the different types of
buffers as they are presented to it. Largely the code path for
metadata will be similar too, but obviously through a different set
of log operations.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index d352b35..db66d32 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -429,13 +429,13 @@
 
 static void discard_buffer(struct gfs2_sbd *sdp, struct buffer_head *bh)
 {
-	struct gfs2_databuf *db;
+	struct gfs2_bufdata *bd;
 
 	gfs2_log_lock(sdp);
-	db = get_v2db(bh);
-	if (db) {
-		db->db_bh = NULL;
-		set_v2db(bh, NULL);
+	bd = get_v2bd(bh);
+	if (bd) {
+		bd->bd_bh = NULL;
+		set_v2bd(bh, NULL);
 		gfs2_log_unlock(sdp);
 		brelse(bh);
 	} else