[Bugfix] Fix tensor shape mismatch in sparse attention with speculative decoding (#39542)

Signed-off-by: Santino Ramos <santinor@inferact.ai>

vllm/model_executor/layers/sparse_attn_indexer.py

@@ -213,7 +213,7 @@ def sparse_attn_indexer(
             )
             torch.ops._C.persistent_topk(
                 logits,
-                decode_metadata.seq_lens,
+                seq_lens,
                 topk_indices,
                 topk_workspace,
                 topk_tokens,
@@ -250,7 +250,7 @@ def sparse_attn_indexer(
                 topk_indices.reshape(batch_size, -1, topk_indices.shape[-1]),
                 decode_lens,
             )
-            topk_indices_buffer[:num_decode_tokens, : topk_indices.shape[-1]] = (
+            topk_indices_buffer[: topk_indices.shape[0], : topk_indices.shape[-1]] = (
                 topk_indices
             )