greybus: audio: Report warning in case module is already removed

Added warning message in find_gb_module(). This will help to identify
invalid mixer control/widget modification triggered from above layer.
Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/audio_topology.c

@@ -47,6 +47,8 @@ static struct gbaudio_module_info *find_gb_module(
 		}
 	}
 	mutex_unlock(&codec->lock);
+	dev_warn(codec->dev, "%s: module#%d missing in codec list\n", name,
+		 dev_id);
 	return NULL;
 }