[XFS] Fix up sparse warnings.

These are mostly locking annotations, marking things static, casts where
needed and declaring stuff in header files.

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30002a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_btree.h b/fs/xfs/xfs_btree.h
index 6e40a0a..7440b78 100644
--- a/fs/xfs/xfs_btree.h
+++ b/fs/xfs/xfs_btree.h
@@ -24,6 +24,8 @@
 struct xfs_mount;
 struct xfs_trans;
 
+extern kmem_zone_t	*xfs_btree_cur_zone;
+
 /*
  * This nonsense is to make -wlint happy.
  */