Tiny fix cutlass_mla_get_workspace_size stub incorrect signature (#7057)

sgl-kernel/csrc/attention/cutlass_mla_kernel.cu

@@ -37,7 +37,7 @@ void cutlass_mla_decode(
     torch::Tensor const& workspace) {
   TORCH_CHECK(false, "CUDA version must be >= 12.4 for cutlass_mla_decode");
 }
-int64_t cutlass_mla_get_workspace_size(int64_t max_seq_len, int64_t num_batches, int64_t sm_count) {
+int64_t cutlass_mla_get_workspace_size(int64_t max_seq_len, int64_t num_batches, int64_t sm_count, int64_t num_kv_splits) {
   TORCH_CHECK(false, "CUDA version must be >= 12.4 for cutlass_mla_get_workspace_size");
 }
 #else