ext4: Avoid double dirtying of super block in ext4_put_super()

While reading code I noticed that ext4_put_super() dirties the 
superblock bh twice. It is always done in ext4_commit_super()
too. Remove the redundant dirty operation.
Should be a nop semantically.
Signed-off-by: Andi Kleen <ak@linux.intel.com>

fs/ext4/super.c

@@ -512,8 +512,6 @@ static void ext4_put_super(struct super_block *sb)
 	if (!(sb->s_flags & MS_RDONLY)) {
 		EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
 		es->s_state = cpu_to_le16(sbi->s_mount_state);
-		BUFFER_TRACE(sbi->s_sbh, "marking dirty");
-		mark_buffer_dirty(sbi->s_sbh);
 		ext4_commit_super(sb, es, 1);
 	}
 	if (sbi->s_proc) {