waylandserver: set render backend for linuxdrmsyncobj directly

The code would previously never set the render backend, causing the use of explicit sync
to fail

BUG: 486391

src/platformsupport/scenes/opengl/abstract_egl_backend.cpp

@@ -192,11 +192,7 @@ void AbstractEglBackend::initWayland()
         LinuxDmaBufV1ClientBufferIntegration *dmabuf = waylandServer()->linuxDmabuf();
         dmabuf->setRenderBackend(this);
         dmabuf->setSupportedFormatsWithModifiers(m_tranches);
-        if (auto syncObj = waylandServer()->linuxSyncObj()) {
-            syncObj->setRenderBackend(this);
-        }
     }
-
     waylandServer()->setRenderBackend(this);
 }
 

src/wayland_server.cpp

@@ -855,6 +855,10 @@ void WaylandServer::setRenderBackend(RenderBackend *backend)
         }
     } else if (m_linuxDrmSyncObj) {
         m_linuxDrmSyncObj->remove();
+        m_linuxDrmSyncObj = nullptr;
+    }
+    if (m_linuxDrmSyncObj) {
+        m_linuxDrmSyncObj->setRenderBackend(backend);
     }
 }