vaapi_h265: cu_qp_delta should not be used in constant-QP mode

libavcodec/vaapi_encode_h265.c

@@ -868,7 +868,10 @@ static int vaapi_encode_h265_init_sequence_params(AVCodecContext *avctx)
 
         vpic->pic_fields.bits.screen_content_flag = 0;
         vpic->pic_fields.bits.enable_gpu_weighted_prediction = 0;
-        vpic->pic_fields.bits.cu_qp_delta_enabled_flag = 1;
+
+        // Per-CU QP changes are required for non-constant-QP modes.
+        vpic->pic_fields.bits.cu_qp_delta_enabled_flag =
+            ctx->va_rc_mode != VA_RC_CQP;
     }
 
     {