convert : fix block_ff_dim retrieval for lfm2 (#21508)

Author: CISC

convert_hf_to_gguf.py

@@ -11818,10 +11818,8 @@ class LFM2Model(TextModel):
     model_arch = gguf.MODEL_ARCH.LFM2
 
     def _add_feed_forward_length(self):
-        ff_dim = self.hparams["block_ff_dim"]
-
+        ff_dim = self.find_hparam(["block_ff_dim", "intermediate_size"])
         auto_adjust_ff_dim = self.hparams["block_auto_adjust_ff_dim"]
-        ff_dim = self.hparams["block_ff_dim"]
         ffn_dim_multiplier = self.hparams["block_ffn_dim_multiplier"]
         multiple_of = self.hparams["block_multiple_of"]