[PATCH 6/6] xfs: rename XFS_BUF_ZEROFLAGS macro

[Christoph Hellwig]

Instead of just renaming it I'd rather dig deeper.

In xlog_bwrite we call xfs_bwrite, which already handles all flag
clearing, so the call to XFS_BUF_ZEROFLAGS can just
be removed.

xlog_sync already sets a lot of these flags again, and is called on an
iclog buffer which never has the READ or XBF_WRITE_FAIL set, so just
replacing it with an opencoded

	bp->b_flags &= (XBF_FUA | XBF_FLUSH);

for both instances should be enough, and even that could be moved
into and else clause of the

	if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)

conditional.