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/btnode.c b/fs/nilfs2/btnode.c
index c353e4f..a35ae35 100644
--- a/fs/nilfs2/btnode.c
+++ b/fs/nilfs2/btnode.c
@@ -254,7 +254,7 @@
 				       "invalid oldkey %lld (newkey=%lld)",
 				       (unsigned long long)oldkey,
 				       (unsigned long long)newkey);
-		nilfs_btnode_mark_dirty(obh);
+		mark_buffer_dirty(obh);
 
 		spin_lock_irq(&btnc->tree_lock);
 		radix_tree_delete(&btnc->page_tree, oldkey);
@@ -266,7 +266,7 @@
 		unlock_page(opage);
 	} else {
 		nilfs_copy_buffer(nbh, obh);
-		nilfs_btnode_mark_dirty(nbh);
+		mark_buffer_dirty(nbh);
 
 		nbh->b_blocknr = newkey;
 		ctxt->bh = nbh;