rust: do not use --generate-cstr

--generate-cstr is a good idea and generally the right thing to do,
but it is not available in Debian 12 and Ubuntu 22.04.  Work around
the absence.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/rust/qemu-api/tests/tests.rs b/rust/qemu-api/tests/tests.rs
index 7442f69..43a4827 100644
--- a/rust/qemu-api/tests/tests.rs
+++ b/rust/qemu-api/tests/tests.rs
@@ -8,7 +8,7 @@
     bindings::*,
     c_str, declare_properties, define_property,
     definitions::{Class, ObjectImpl},
-    device_class_init,
+    device_class, device_class_init,
     zeroable::Zeroable,
 };
 
@@ -57,7 +57,7 @@ impl ObjectImpl for DummyState {
         type Class = DummyClass;
         const TYPE_INFO: qemu_api::bindings::TypeInfo = qemu_api::type_info! { Self };
         const TYPE_NAME: &'static CStr = c_str!("dummy");
-        const PARENT_TYPE_NAME: Option<&'static CStr> = Some(TYPE_DEVICE);
+        const PARENT_TYPE_NAME: Option<&'static CStr> = Some(device_class::TYPE_DEVICE);
         const ABSTRACT: bool = false;
         const INSTANCE_INIT: Option<unsafe extern "C" fn(obj: *mut Object)> = None;
         const INSTANCE_POST_INIT: Option<unsafe extern "C" fn(obj: *mut Object)> = None;