firmware: cs_dsp: Remove need for clients to supply

Merge series from Richard Fitzgerald <[e-mail]>:

Clients of cs_dsp can provide optional callback function pointers, in
a struct cs_dsp_client_ops. The client had to provide a pointer to a
struct even if it didn't implement any of the callbacks.

drivers/firmware/cirrus/cs_dsp.c

···
 	return 0;
 }
 
+static const struct cs_dsp_client_ops cs_dsp_default_client_ops = {
+};
+
 static int cs_dsp_common_init(struct cs_dsp *dsp)
 {
 	int ret;
···
 	INIT_LIST_HEAD(&dsp->ctl_list);
 
 	mutex_init(&dsp->pwr_lock);
+
+	if (!dsp->client_ops)
+		dsp->client_ops = &cs_dsp_default_client_ops;
 
 #ifdef CONFIG_DEBUG_FS
 	/* Ensure this is invalid if client never provides a debugfs root */

drivers/firmware/cirrus/test/cs_dsp_test_callbacks.c

···
 
 static const struct cs_dsp_callbacks_test_param cs_dsp_no_callbacks_cases[] = {
 	{ .ops =  &cs_dsp_callback_test_empty_client_ops, .case_name = "empty ops" },
+	{ .ops =  NULL, .case_name = "NULL ops" },
 };
 
 KUNIT_ARRAY_PARAM(cs_dsp_no_callbacks,