Fix forward pass in UNetMotionModel when gradient checkpoint is enabled (#6744)

fix #6742
Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>

src/diffusers/models/unets/unet_3d_blocks.py

@@ -1031,12 +1031,6 @@ class DownBlockMotion(nn.Module):
                     hidden_states = torch.utils.checkpoint.checkpoint(
                         create_custom_forward(resnet), hidden_states, temb, scale
                     )
-                hidden_states = torch.utils.checkpoint.checkpoint(
-                    create_custom_forward(motion_module),
-                    hidden_states.requires_grad_(),
-                    temb,
-                    num_frames,
-                )
 
             else:
                 hidden_states = resnet(hidden_states, temb, scale=scale)
@@ -1563,11 +1557,6 @@ class UpBlockMotion(nn.Module):
                     hidden_states = torch.utils.checkpoint.checkpoint(
                         create_custom_forward(resnet), hidden_states, temb
                     )
-                hidden_states = torch.utils.checkpoint.checkpoint(
-                    create_custom_forward(resnet),
-                    hidden_states,
-                    temb,
-                )
 
             else:
                 hidden_states = resnet(hidden_states, temb, scale=scale)