xfs: constify xfs_item_ops

The log item ops aren't nessecarily the biggest exploit vector, but marking
them const is easy enough.  Also remove the unused xfs_item_ops_t typedef
while we're at it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 2758a62..a14cd89 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -626,7 +626,7 @@
 	struct xfs_mount	*mp,
 	struct xfs_log_item	*item,
 	int			type,
-	struct xfs_item_ops	*ops)
+	const struct xfs_item_ops *ops)
 {
 	item->li_mountp = mp;
 	item->li_ailp = mp->m_ail;