constify dentry_operations: NFS

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index 4e4d332..84345de 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -179,7 +179,7 @@
 	int (*recover_lock)(struct nfs4_state *, struct file_lock *);
 };
 
-extern struct dentry_operations nfs4_dentry_operations;
+extern const struct dentry_operations nfs4_dentry_operations;
 extern const struct inode_operations nfs4_dir_inode_operations;
 
 /* inode.c */