Update ddpm.py

Change:
from pytorch_lightning.utilities.distributed import rank_zero_only
to:
from pytorch_lightning.utilities.rank_zero import rank_zero_only

ldm/models/diffusion/ddpm.py

@@ -16,8 +16,8 @@ from contextlib import contextmanager
 from functools import partial
 from tqdm import tqdm
 from torchvision.utils import make_grid
-from pytorch_lightning.utilities.distributed import rank_zero_only
+#from pytorch_lightning.utilities.distributed import rank_zero_only
-
+from pytorch_lightning.utilities.rank_zero import rank_zero_only 
 from ldm.util import log_txt_as_img, exists, default, ismap, isimage, mean_flat, count_params, instantiate_from_config
 from ldm.modules.ema import LitEma
 from ldm.modules.distributions.distributions import normal_kl, DiagonalGaussianDistribution