[Bugfix] fix tmp_out and exp_sums dimensions (#17438)

Signed-off-by: Hui Liu <96135754+hliuca@users.noreply.github.com>

vllm/attention/ops/chunked_prefill_paged_decode.py

@@ -289,7 +289,7 @@ def chunked_prefill_paged_decode(
         max_num_partitions = ((max_seq_len + _PARTITION_SIZE_ROCM - 1) //
                               _PARTITION_SIZE_ROCM)
         assert _PARTITION_SIZE_ROCM % block_size == 0
-        total_num_seq = query.shape[0]
+        total_num_seq = block_table.shape[0]
         tmp_output = torch.empty(
             size=(total_num_seq, num_query_heads, max_num_partitions,
                   head_size),