constify dentry_operations: NFS

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index db867b0..8cc8807 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -415,7 +415,7 @@
 extern const struct inode_operations nfs3_dir_inode_operations;
 #endif /* CONFIG_NFS_V3 */
 extern const struct file_operations nfs_dir_operations;
-extern struct dentry_operations nfs_dentry_operations;
+extern const struct dentry_operations nfs_dentry_operations;
 
 extern void nfs_force_lookup_revalidate(struct inode *dir);
 extern int nfs_instantiate(struct dentry *dentry, struct nfs_fh *fh, struct nfs_fattr *fattr);