ACPI video: correct error-handling code

backlight_device_register may return an ERR_PTR
value rather than a valid pointer.

Problem found by Julia Lawall, properly fixed by Zhang Rui.
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/video.c

@@ -999,8 +999,10 @@ static void acpi_video_device_find_cap(struct acpi_video_device *device)
 		sprintf(name, "acpi_video%d", count++);
 		device->backlight = backlight_device_register(name,
 			NULL, device, &acpi_backlight_ops);
-		device->backlight->props.max_brightness = device->brightness->count-3;
 		kfree(name);
+		if (IS_ERR(device->backlight))
+			return;
+		device->backlight->props.max_brightness = device->brightness->count-3;
 
 		result = sysfs_create_link(&device->backlight->dev.kobj,
 					   &device->dev->dev.kobj, "device");