ocfs2: Fix estimate of necessary credits for mkdir

In the rare case that INLINE_DATA, INDEX_DIR, QUOTA, XATTR features are
disabled and both the allocation of the directory inode and the allocation
of the first directory block need to relink allocation group, there need
not be enough credits reserved in a transaction. Fix the estimate.

CC: Mark Fasheh <mfasheh@suse.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Joel Becker <jlbec@evilplan.org>