CUDA: Fix ssm_scan_f32 data-races (ggml-org#24360)

* Add missing syncthreads before resuing cub_temp_storage

__syncthreads() is required before being allowed to resue TempStorage
smem:
https://nvidia.github.io/cccl/unstable/cub/api/classcub_1_1BlockLoad.html#_CPPv4I0EN3cub9BlockLoad4LoadEv20RandomAccessIteratorRA14ItemsPerThread_1Ti

* Add one more missing __syncthreads

Could also double-buffer, but alternative is to simply ensure all
threads have read smem* before writing to it again in the next loop
iteration

* Remove unused smem from ssm_scan_f32

Author: ORippler

ggml/src/ggml-cuda/ssm-scan.cu

@@ -67,6 +67,7 @@ __global__ void __launch_bounds__(splitD, 1)
     __shared__ CubTempStorage cub_temp_storage;
 
     BlockLoad(cub_temp_storage.load_temp).Load(A_block, regA);
+    __syncthreads();
     BlockLoad(cub_temp_storage.load_temp).Load(s0_block, regs0);
 #else
     const int stride_s0 = src0_nb2 / sizeof(float);
@@ -105,6 +106,7 @@ __global__ void __launch_bounds__(splitD, 1)
             regs0[n] = state;
         }
         y_block[i * stride_y + threadIdx.x] = sumf;
+        __syncthreads();
     }
 
 #ifdef USE_CUB
@@ -249,9 +251,8 @@ static void ssm_scan_f32_cuda(const float * src0, const float * src1, const floa
         GGML_ASSERT(head_dim == 1);
         GGML_ASSERT(n_group == 1);
         const dim3 blocks(n_seq, (n_head + threads - 1) / threads, 1);
-        const int  smem_size = (threads * (d_state + 1) * 2) * sizeof(float);
         if (d_state == 16) {
-            const ggml_cuda_kernel_launch_params launch_params = ggml_cuda_kernel_launch_params(blocks, threads, smem_size, stream);
+            const ggml_cuda_kernel_launch_params launch_params = ggml_cuda_kernel_launch_params(blocks, threads, 0, stream);
             switch (n_tok)
             {
             case 1: