xfs: move declaration to header file

Fix this sparse warning:
  fs/xfs/xfs_da_btree.c:1550:26: warning: symbol 'xfs_default_nameops' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Felix Blyakher <felixb@sgi.com>
diff --git a/fs/xfs/xfs_da_btree.h b/fs/xfs/xfs_da_btree.h
index 9d5a7e8..41f27b3 100644
--- a/fs/xfs/xfs_da_btree.h
+++ b/fs/xfs/xfs_da_btree.h
@@ -268,5 +268,6 @@
 
 extern struct kmem_zone *xfs_da_state_zone;
 extern struct kmem_zone *xfs_dabuf_zone;
+extern const struct xfs_nameops xfs_default_nameops;
 
 #endif	/* __XFS_DA_BTREE_H__ */