ACPI / video: Inline acpi_video_set_dmi_backlight_type

... and kill this:

  In file included from drivers/gpu/drm/radeon/radeon_acpi.c:29:0:
  include/acpi/video.h:46:13: warning: ‘acpi_video_set_dmi_backlight_type’ defined but not used [-Wunused-function]
   static void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
               ^
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/acpi/video.h

@@ -43,7 +43,7 @@ static inline enum acpi_backlight_type acpi_video_get_backlight_type(void)
 {
 	return acpi_backlight_vendor;
 }
-static void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
+static inline void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
 {
 }
 #endif