constify dentry_operations: autofs, autofs4

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/autofs/root.c b/fs/autofs/root.c
index 8aacade..4a1401c 100644
--- a/fs/autofs/root.c
+++ b/fs/autofs/root.c
@@ -192,7 +192,7 @@
 	return 1;
 }
 
-static struct dentry_operations autofs_dentry_operations = {
+static const struct dentry_operations autofs_dentry_operations = {
 	.d_revalidate	= autofs_revalidate,
 };