Fix moved _expand_mask function (huggingface#5581)

* finish

* finish

src/diffusers/pipelines/blip_diffusion/modeling_ctx_clip.py

@@ -19,10 +19,21 @@
 from transformers import CLIPPreTrainedModel
 from transformers.modeling_outputs import BaseModelOutputWithPooling
 from transformers.models.clip.configuration_clip import CLIPTextConfig
-from transformers.models.clip.modeling_clip import (
-    CLIPEncoder,
-    _expand_mask,
-)
+from transformers.models.clip.modeling_clip import CLIPEncoder
+
+
+def _expand_mask(mask: torch.Tensor, dtype: torch.dtype, tgt_len: Optional[int] = None):
+    """
+    Expands attention_mask from `[bsz, seq_len]` to `[bsz, 1, tgt_seq_len, src_seq_len]`.
+    """
+    bsz, src_len = mask.size()
+    tgt_len = tgt_len if tgt_len is not None else src_len
+
+    expanded_mask = mask[:, None, None, :].expand(bsz, 1, tgt_len, src_len).to(dtype)
+
+    inverted_mask = 1.0 - expanded_mask
+
+    return inverted_mask.masked_fill(inverted_mask.to(torch.bool), torch.finfo(dtype).min)
 
 
 # This is a modified version of the CLIPTextModel from transformers.models.clip.modeling_clip