drm/radeon/audio: make sure connector is valid in hotplug case

Avoids a crash when a monitor is hotplugged and the encoder
and connector are not linked yet.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=90681

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/evergreen_hdmi.c

@@ -400,7 +400,7 @@ void evergreen_hdmi_enable(struct drm_encoder *encoder, bool enable)
 	if (enable) {
 		struct drm_connector *connector = radeon_get_connector_for_encoder(encoder);
 
-		if (drm_detect_monitor_audio(radeon_connector_edid(connector))) {
+		if (connector && drm_detect_monitor_audio(radeon_connector_edid(connector))) {
 			WREG32(HDMI_INFOFRAME_CONTROL0 + dig->afmt->offset,
 			       HDMI_AVI_INFO_SEND | /* enable AVI info frames */
 			       HDMI_AVI_INFO_CONT | /* required for audio info values to be updated */
@@ -438,7 +438,8 @@ void evergreen_dp_enable(struct drm_encoder *encoder, bool enable)
 	if (!dig || !dig->afmt)
 		return;
 
-	if (enable && drm_detect_monitor_audio(radeon_connector_edid(connector))) {
+	if (enable && connector &&
+	    drm_detect_monitor_audio(radeon_connector_edid(connector))) {
 		struct drm_connector *connector = radeon_get_connector_for_encoder(encoder);
 		struct radeon_connector *radeon_connector = to_radeon_connector(connector);
 		struct radeon_connector_atom_dig *dig_connector;