refactor: simplify sliding window sparse config logic

Streamline the assignment of sparse_mode, pre_tokens, and next_tokens
when configuring sliding window attention.

Signed-off-by: vv <939082363@qq.com>

Author: vvaen

vllm_ascend/attention/attention_v1.py

@@ -618,16 +618,9 @@ def full_graph_fia(
         softmax_lse = torch.empty(1, dtype=query.dtype, device=query.device)
         input_layout = "TND"
         attn_mask = attn_metadata.attn_mask
-
-        if self.sliding_window is not None:
-            sparse_mode = 4
-            pre_tokens = self.sliding_window
-            next_tokens = 0
-
-        else:
-            sparse_mode = 3 if attn_metadata.causal else 0
-            pre_tokens = SWA_INT_MAX
-            next_tokens = SWA_INT_MAX
+        sparse_mode = 4 if self.sliding_window else 3 if attn_metadata.causal else 0
+        pre_tokens = self.sliding_window or SWA_INT_MAX
+        next_tokens= 0 if self.sliding_window else SWA_INT_MAX
 
         extra_args = {}
         if self.enable_c8_quant: