[Fix] Wait for PDL before reading DeepSeek V4 K cache locations (#38409)

Co-authored-by: Aurick Qiao <6137920+aurickq@users.noreply.github.com>

python/sglang/kernels/jit/csrc/deepseek_v4/main_norm_rope.cuh

@@ -280,10 +280,10 @@ K_KERNEL void fused_k_norm_rope_flashmla(const __grid_constant__ FusedKNormRopeF
 
   const auto input_ptr = static_cast<const DType*>(params.kv) + work_id * params.kv_stride_batch;
   const auto position = static_cast<int32_t>(static_cast<const PosT*>(params.positions)[work_id]);
-  const auto out_loc = params.out_loc[work_id];
   const auto freqs_cis = params.freqs_cis + position * kRopeDim;
 
   PDLWaitPrimary<kUsePDL>();
+  const auto out_loc = params.out_loc[work_id];
   Float2 data, freq;
 
   // part 1: norm. Each thread owns one 2-elem pack (the `tx`-th).