message: Fix bug in cuddn_fused_conv_rewriter.
  The scale for the convolution result and for the side input must be scalar constants.
  Before this change, any constant would be accepted.
diff: @@ -44,7 +44,7 @@ absl::optional<ConvWithRelu> FindConvWithRelu(HloInstruction* instr) {
  using match::AddAnyOrder;
  using match::AnyOf;
  using match::Broadcast;
  - using match::Constant;
  + using match::ConstantScalar;
  using match::GetTupleElement;
  using match::Maximum;
  using match::MultiplyAnyOrder;
  @@ -59,7 +59,7 @@ absl::optional<ConvWithRelu> FindConvWithRelu(HloInstruction* instr) {
  HloInstruction* relu_input;
  // Match max(0, relu_input).
  - auto zero_pattern = Broadcast(match::ConstantScalar(0));
  + auto zero_pattern = Broadcast(ConstantScalar(0));
  if (!Match(instr, Maximum(zero_pattern, Op(&relu_input))) &&
  !Match(instr, Maximum(Op(&relu_input), zero_pattern))) {
  return absl::nullopt;
  @@ -78,14 +78,14 @@ absl::optional<ConvWithRelu> FindConvWithRelu(HloInstruction* instr) {
  const auto bias_pattern = Broadcast(&bias_broadcast_instr, Op(&bias));
  const auto conv_pattern = [&] {
  - auto alpha_pattern = Broadcast(Constant(&alpha_conv_instr));
  + auto alpha_pattern = Broadcast(ConstantScalar(&alpha_conv_instr));
  auto conv_pattern = GetTupleElement(
  &gte, Op(&conv_instr).WithOpcode(HloOpcode::kCustomCall), 0);
  return AnyOf<HloInstruction>(
  MultiplyAnyOrder(&mul1, alpha_pattern, conv_pattern), conv_pattern);
  }();
  const auto side_input_pattern = [&] {
  - auto alpha_pattern = Broadcast(Constant(&alpha_side_input_instr));
  + auto alpha_pattern = Broadcast(ConstantScalar(&alpha_side_input_instr));
  // If bias is already matched, match arbitrary additional input as side
  // input. Note this may force a cheap operation (e.g. broadcast) to be
  // materialized into a large buffer, as large as the output buffer.
  