[Model][QwenVL] Simplify cos/sin rotary embedding indexing (#28962)

Signed-off-by: Lukas Geiger <lukas.geiger94@gmail.com>

vllm/model_executor/models/qwen3_omni_moe_thinker.py

@@ -428,13 +428,8 @@ class Qwen3Omni_VisionTransformer(nn.Module):
         # Use pre-computed cos_sin_cache from RotaryEmbedding
         cos, sin = self.rotary_pos_emb.get_cos_sin(max_grid_size)
 
-        cos_h = cos[pos_ids[:, 0]]  # (num_tokens, rotary_dim // 2)
-        cos_w = cos[pos_ids[:, 1]]
-        sin_h = sin[pos_ids[:, 0]]
-        sin_w = sin[pos_ids[:, 1]]
-
-        cos_combined = torch.cat([cos_h, cos_w], dim=-1)
-        sin_combined = torch.cat([sin_h, sin_w], dim=-1)
+        cos_combined = cos[pos_ids].flatten(1)
+        sin_combined = sin[pos_ids].flatten(1)
 
         return cos_combined, sin_combined