nilfs2: use mark_buffer_dirty to mark btnode or meta data dirty

This replaces nilfs_mdt_mark_buffer_dirty and nilfs_btnode_mark_dirty
macros with mark_buffer_dirty and gets rid of nilfs_mark_buffer_dirty,
an own mark buffer dirty function.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index eeb1bc2..141646e 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -806,7 +806,7 @@
 		/* The following code is duplicated with cpfile.  But, it is
 		   needed to collect the checkpoint even if it was not newly
 		   created */
-		nilfs_mdt_mark_buffer_dirty(bh_cp);
+		mark_buffer_dirty(bh_cp);
 		nilfs_mdt_mark_dirty(nilfs->ns_cpfile);
 		nilfs_cpfile_put_checkpoint(
 			nilfs->ns_cpfile, nilfs->ns_cno, bh_cp);
@@ -1865,7 +1865,7 @@
 					      "failed to get inode block.\n");
 				return err;
 			}
-			nilfs_mdt_mark_buffer_dirty(ibh);
+			mark_buffer_dirty(ibh);
 			nilfs_mdt_mark_dirty(ifile);
 			spin_lock(&nilfs->ns_inode_lock);
 			if (likely(!ii->i_bh))