Fix config default for LM

Without this setting downstream packages like MLX-VLM fail to load QK_NORM.

config.json

@@ -61,6 +61,7 @@
     "sliding_window": null,
     "use_cache": true,
     "use_sliding_window": false,
+    "use_qk_norm": true,
     "tie_word_embeddings": true,
     "vocab_size": 151936
   },