DetectMultiBackend() return `device` update (#6958)

Fixes ONNX validation that returns outputs on CPU.

models/common.py

@@ -458,7 +458,8 @@ class DetectMultiBackend(nn.Module):
                     y = (y.astype(np.float32) - zero_point) * scale  # re-scale
             y[..., :4] *= [w, h, w, h]  # xywh normalized to pixels
 
-        y = torch.tensor(y) if isinstance(y, np.ndarray) else y
+        if isinstance(y, np.ndarray):
+            y = torch.tensor(y, device=self.device)
         return (y, []) if val else y
 
     def warmup(self, imgsz=(1, 3, 640, 640)):