Actually the simpler fix for this in case of fast commits is to check
if the inode is on the fast commit list or not. Since we clear the
fast commit list after every fast and / or full commit, it's always
true that if the inode is not on the list, that means it isn't dirty.
This will simplify the logic here and then we can probably get rid of
i_fc_committed_subtid field altogether. I'll test this and send out a
patch.