fix: mha_varlen_fwd not support

src/SanaModel.cpp

@@ -180,7 +180,7 @@ Tensor MultiHeadCrossAttention::forward(Tensor x, Tensor cond, Tensor cu_seqlens
     //                                     false)
     //                          .front()
     //                          .view({batch_size, num_tokens_img, num_heads * head_dim});
-    Tensor attn_output = Tensor::ones({batch_size * num_tokens, num_heads, dim_head}, Tensor::FP16, Device::cuda());    
+    Tensor attn_output = Tensor::ones({batch_size, num_tokens_img, num_heads * head_dim}, Tensor::FP16, Device::cuda());
     std::cout << "mha_varlen_fwd not support !!!" << std::endl;
     // Tensor attn_output = mha_fwd(q, k, v,
     //     0.0f,