[Perf] Optimize dcp allocate tensor (#33102)

Signed-off-by: yewentao256 <zhyanwentao@126.com>

vllm/v1/attention/ops/common.py

@@ -195,14 +195,10 @@ def _cp_lse_common(
     if ctx is None:
         ctx = CPTritonContext()
 
-    lses = torch.empty(
-        (cp_group.world_size,) + cp_attn_lse.shape,
-        dtype=cp_attn_lse.dtype,
-        device=cp_attn_lse.device,
-    )
-
     cp_attn_lse = cp_attn_lse.contiguous()
-    lses = cp_group.all_gather(cp_attn_lse, dim=0).view_as(lses)
+    lses = cp_group.all_gather(cp_attn_lse, dim=0).reshape(
+        (cp_group.world_size,) + cp_attn_lse.shape
+    )
     out, lse = correct_attn_out(
         cp_attn_out,
         lses,