ACPI / video: Fix using an uninitialized mutex / list_head in acpi_video_handles_brightness_key_presses()

If acpi_video_handles_brightness_key_presses() was called before
acpi_video_register(), it would use the video_list mutex / list_head
uninitialized.

This patch fixes this by using DEFINE_MUTEX / LIST_HEAD when declaring
these, instead of initializing them runtime from acpi_video_register().

Fixes: 90b066b15eda "ACPI / video: Add a acpi_video_handles_brightness_key_presses() helper"
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_video.c

@@ -92,8 +92,8 @@ module_param(only_lcd, bool, 0444);
 
 static int register_count;
 static DEFINE_MUTEX(register_count_mutex);
-static struct mutex video_list_lock;
-static struct list_head video_bus_head;
+static DEFINE_MUTEX(video_list_lock);
+static LIST_HEAD(video_bus_head);
 static int acpi_video_bus_add(struct acpi_device *device);
 static int acpi_video_bus_remove(struct acpi_device *device);
 static void acpi_video_bus_notify(struct acpi_device *device, u32 event);
@@ -2067,9 +2067,6 @@ int acpi_video_register(void)
 		goto leave;
 	}
 
-	mutex_init(&video_list_lock);
-	INIT_LIST_HEAD(&video_bus_head);
-
 	dmi_check_system(video_dmi_table);
 
 	ret = acpi_bus_register_driver(&acpi_video_bus);