handle dtype xformers attention (#1196)

handle dtype xformers

src/diffusers/models/attention.py

@@ -492,6 +492,8 @@ class CrossAttention(nn.Module):
         # attention, what we cannot get enough of
         if self._use_memory_efficient_attention_xformers:
             hidden_states = self._memory_efficient_attention_xformers(query, key, value)
+            # Some versions of xformers return output in fp32, cast it back to the dtype of the input
+            hidden_states = hidden_states.to(query.dtype)
         else:
             if self._slice_size is None or query.shape[0] // self._slice_size == 1:
                 hidden_states = self._attention(query, key, value)