hfsplus: get rid of write_super

This patch makes hfsplus stop using the VFS '->write_super()' method along with
the 's_dirt' superblock flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblocks using the '->write_super()' call-back.  But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Tested using fsstress from the LTP project.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/hfsplus/dir.c b/fs/hfsplus/dir.c
index 378ea0c..6b9f921 100644
--- a/fs/hfsplus/dir.c
+++ b/fs/hfsplus/dir.c
@@ -316,7 +316,7 @@
 	inode->i_ctime = CURRENT_TIME_SEC;
 	mark_inode_dirty(inode);
 	sbi->file_count++;
-	dst_dir->i_sb->s_dirt = 1;
+	hfsplus_mark_mdb_dirty(dst_dir->i_sb);
 out:
 	mutex_unlock(&sbi->vh_mutex);
 	return res;