fix(schedulers): same device on DDPMScheduler

make sure variance is on same device as model output in the  method

src/schedulers/ddpm.rs

@@ -167,9 +167,10 @@ impl DDPMScheduler {
 
         // https://github.com/huggingface/diffusers/blob/df2b548e893ccb8a888467c2508756680df22821/src/diffusers/schedulers/scheduling_ddpm.py#L305
         // 6. Add noise
-        let mut variance = Tensor::zeros(&pred_prev_sample.size(), kind::FLOAT_CPU);
+        let (device, dtype) = (model_output.device(), model_output.kind());
+        let mut variance = Tensor::zeros(&model_output.size(), (dtype, device));
         if timestep > 0 {
-            let variance_noise = Tensor::randn_like(model_output);
+            let variance_noise = model_output.randn_like();
             if self.config.variance_type == DDPMVarianceType::FixedSmallLog {
                 variance = self.get_variance(timestep) * variance_noise;
             } else {