Fix starcoder first token perf (#10612)

* add bias check

* update

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

@@ -538,7 +538,7 @@ def __init__(self, input_features, output_features, qtype, bias=True,
         # The condition makes sure that empty cache only takes effect if this layer is lm_head.
         # For other models like llama, lm_cache will be applied as well
         # since performance isn't impacted.
-        self.is_lm_head = self.in_len * self.out_len >= 30000 * 4096
+        self.is_lm_head = self.in_len * self.out_len >= 32000 * 4096 and self.bias is None
         self.low_memory_mode = self.is_lm_head
 
     def forward(self, x: torch.Tensor):