Fix slow tests (#689)

* revert using baddbmm in attention
- to fix `test_stable_diffusion_memory_chunking` test

* styling

src/diffusers/models/attention.py

@@ -274,13 +274,8 @@ class CrossAttention(nn.Module):
         return self.to_out(hidden_states)
 
     def _attention(self, query, key, value):
-        attention_scores = torch.baddbmm(
-            torch.empty(query.shape[0], query.shape[1], key.shape[1], dtype=query.dtype, device=query.device),
-            query,
-            key.transpose(-1, -2),
-            beta=0,
-            alpha=self.scale,
-        )
+        # TODO: use baddbmm for better performance
+        attention_scores = torch.matmul(query, key.transpose(-1, -2)) * self.scale
         attention_probs = attention_scores.softmax(dim=-1)
         # compute attention output
         hidden_states = torch.matmul(attention_probs, value)