docs : fix DSpark confidence threshold flag name (--spec-draft-p-min) (#31178)

docs/speculative.md

@@ -100,8 +100,9 @@ llama-server -m Qwen3-4B.gguf -md Qwen3-4B-DSpark.gguf \
 
 `--spec-draft-n-max` is clamped to the draft model's trained block size.
 
-`--spec-draft-conf-min P` truncates each drafted block at the first position whose predicted
-acceptance (from the draft's confidence head, if present) falls below `P` (default 0 = disabled).
+`--spec-draft-p-min P` truncates each drafted block at the first position whose predicted
+acceptance (from the draft's confidence head) falls below `P` (default 0 = disabled).
+Values above 0 require a draft with a confidence head.
 
 Currently only drafts with a Qwen3 backbone are supported; support for other backbones
 (e.g. Gemma4) is planned.