drm/amd/display: Avoid MST manager resource leak.

commit 5dff80b upstream.

On connector destruction call drm_dp_mst_topology_mgr_destroy
to release resources allocated in drm_dp_mst_topology_mgr_init.
Do it only if MST manager was initilized before otherwsie a crash
is seen on driver unload/device unplug.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Andrey Grodzovsky

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4882,6 +4882,13 @@ static void amdgpu_dm_connector_destroy(struct drm_connector *connector)
 	struct amdgpu_device *adev = connector->dev->dev_private;
 	struct amdgpu_display_manager *dm = &adev->dm;
 
+	/*
+	 * Call only if mst_mgr was iniitalized before since it's not done
+	 * for all connector types.
+	 */
+	if (aconnector->mst_mgr.dev)
+		drm_dp_mst_topology_mgr_destroy(&aconnector->mst_mgr);
+
 #if defined(CONFIG_BACKLIGHT_CLASS_DEVICE) ||\
 	defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE)