[bugfix] some bugs maybe fail to run (#896)

### What this PR does / why we need it?
Solve the bug that the graph mode is the same as p and d, and some other
bugs.
### Does this PR introduce _any_ user-facing change?
Wouldn't be
### How was this patch tested?
Follow the end-to-end test

Signed-off-by: ningbenzhe1 <ningbenzhe@huawei.com>

tests/long_term/spec_decode/e2e/test_v1_mtp_correctness.py

@@ -89,4 +89,4 @@ def test_mtp_correctness(
         # Heuristic: expect at least 66% of the prompts to match exactly
         # Upon failure, inspect the outputs to check for inaccuracy.
         assert matches > int(0.66 * len(ref_outputs))
-        del spec_llm
+        del spec_llm