audio: mic_privacy_manager: Fix NULL pointer dereference in ZTest

Add null checks for hardware device pointers that may not be
available when running in ZTest environments without real hardware.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

src/audio/mic_privacy_manager/mic_privacy_manager_intel.c

@@ -95,6 +95,11 @@ int mic_privacy_manager_init(void)
 	if (!mic_priv_dev)
 		return -EINVAL;
 
+	if (!device_is_ready(mic_priv_dev)) {
+		LOG_ERR("mic_privacy device not ready");
+		return -ENODEV;
+	}
+
 	mic_privacy_api = (struct mic_privacy_api_funcs *)mic_priv_dev->api;
 	mic_privacy_policy = mic_privacy_api->get_policy();
 
@@ -109,6 +114,9 @@ int mic_privacy_manager_init(void)
 
 int mic_privacy_manager_get_policy(void)
 {
+	if (!mic_priv_dev)
+		return MIC_PRIVACY_HW_MANAGED;
+
 	mic_privacy_api = (struct mic_privacy_api_funcs *)mic_priv_dev->api;
 
 	return mic_privacy_api->get_policy();