drm: do not debug log about missing CEA extensions on NULL edid

Make the drm_edid_to_eld() function useful for resetting, not just
setting, the ELD and HDMI VSDB data, without debug warnings about
missing CEA extensions.
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487344854-18777-3-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c

@@ -3437,6 +3437,9 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
 	connector->video_latency[1] = 0;
 	connector->audio_latency[1] = 0;
 
+	if (!edid)
+		return;
+
 	cea = drm_find_cea_extension(edid);
 	if (!cea) {
 		DRM_DEBUG_KMS("ELD: no CEA Extension found\n");