drm/i915: Don't complain about lack of ACPI video bios

Another CI fail we have for no reason. Totally unjustified since
nothing fails at all.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1445590806-23886-1-git-send-email-daniel.vetter@ffwll.ch
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_opregion.c

@@ -682,7 +682,7 @@ static void intel_didl_outputs(struct drm_device *dev)
 	}
 
 	if (!acpi_video_bus) {
-		DRM_ERROR("No ACPI video bus found\n");
+		DRM_DEBUG_KMS("No ACPI video bus found\n");
 		return;
 	}