video / backlight: remove the backlight_device_registered API

Since we will need the backlight_device_get_by_type API, we can use it
instead of the backlight_device_registered API whenever necessary so
remove the backlight_device_registered API.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 1316ddd..3d13276 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -358,7 +358,7 @@
 	if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
 		return acpi_backlight_vendor;
 
-	if (acpi_osi_is_win8() && backlight_device_registered(BACKLIGHT_RAW))
+	if (acpi_osi_is_win8() && backlight_device_get_by_type(BACKLIGHT_RAW))
 		return acpi_backlight_native;
 
 	return acpi_backlight_video;