Fix wrong attention mask and garbage output for inputs_embeds inputs during lookup generation (#11989)

* Fix garbage output for input_embeds inputs during lookup generation

* Fix on sliding windows

* Simplify code

python/llm/src/ipex_llm/transformers/lookup.py

@@ -175,7 +175,7 @@ class PromptLookupCandidateGenerator():
 
     def init_look_up_table(self,
                            input_ids: torch.LongTensor):
-        for ngram_size in range(self.max_matching_ngram_size, 0, -1):
+        for ngram_size in range(min(self.max_matching_ngram_size, input_ids.shape[1]), 0, -1):
             # Create sliding windows of size ngram_size
             windows = input_ids.cpu().unfold(dimension=1, size=ngram_size, step=1)
             for idx in range(windows.size(1)):
@@ -315,11 +315,9 @@ def lookup_generate(self,
         if step == 0:
             # first token use full model
             tic = time.time()
-            output = self(input_ids=input_ids,
-                          past_key_values=past_key_values,
-                          attention_mask=attention_mask,
-                          return_dict=True,
-                          use_cache=True)
+            model_inputs = self.prepare_inputs_for_generation(input_ids, **model_kwargs)
+            output = self(**model_inputs,
+                          return_dict=True)
             logits = output['logits']
             logits = logits[:, -1:]
             logits[:, -1, :] = logits_processor(input_ids, logits[:, -1, :])