[XPU]Fix flash_attn_varlen_func interface on xpu (#22350)

Signed-off-by: Kunshang Ji <kunshang.ji@intel.com>

vllm/_ipex_ops.py

@@ -271,6 +271,7 @@ class ipex_ops:
         k_descale=None,
         v_descale=None,
         num_splits=0,
+        s_aux: Optional[torch.Tensor] = None,
     ):
         if cu_seqlens_k is None:
             # cu_seqlens_k is not used in ipex kernel.