drm: remember to clean up DrmGpu's outputs when destroying

src/plugins/platforms/drm/drm_gpu.cpp

@@ -89,6 +89,7 @@ DrmGpu::~DrmGpu()
         gbm_device_destroy(m_gbmDevice);
     }
 #endif
+    qDeleteAll(m_outputs);
     qDeleteAll(m_crtcs);
     qDeleteAll(m_connectors);
     qDeleteAll(m_planes);