fix (#5945)

Co-authored-by: Noneflow-ci-bot <69100618+oneflow-ci-bot@users.noreply.github.com>

oneflow/core/autograd/gradient_funcs/matmul.cpp

@@ -180,13 +180,13 @@ Maybe<void> BroadcastMatmul::Apply(const MatmulInterpState* ctx, const TensorTup
   JUST(attrs_b.SetAttr<double>("alpha", ctx->alpha));
 
   in_grads->resize(2);
-  if (ctx->requires_grad_b) {
+  if (ctx->requires_grad_a) {
     const auto& input_b = ctx->SavedTensors().at(ctx->b_index);
     in_grads->at(0) =
         JUST(OpInterpUtil::Dispatch<Tensor>(*grad_a_op_, {out_grads.at(0), input_b}, attrs_a));
   }
 
-  if (ctx->requires_grad_a) {
+  if (ctx->requires_grad_b) {
     const auto& input_a = ctx->SavedTensors().at(ctx->a_index);
     if (!ctx->transpose_b) {
       in_grads->at(1) =