Simplify flashinfer utilities (#1704)

python/sglang/srt/managers/schedule_batch.py

@@ -744,7 +744,6 @@ class ScheduleBatch:
         self.forward_mode = ForwardMode.DECODE
 
         self.input_ids = self.output_ids
-        self.seq_lens.add_(1)
         self.output_ids = None
         if self.sampling_info.penalizer_orchestrator:
             self.sampling_info.penalizer_orchestrator.cumulate_output_tokens(
@@ -755,9 +754,10 @@ class ScheduleBatch:
         bs = len(self.reqs)
         self.out_cache_loc = self.alloc_token_slots(bs)
 
-        self.req_to_token_pool.req_to_token[
-            self.req_pool_indices, self.seq_lens - 1
-        ] = self.out_cache_loc
+        self.req_to_token_pool.req_to_token[self.req_pool_indices, self.seq_lens] = (
+            self.out_cache_loc
+        )
+        self.seq_lens.add_(1)
 
     def filter_batch(
         self,