Fix a dimension bug in Transform2d (#2144)

The dimension does not match when `inner_dim` is not equal to `in_channels`.

src/diffusers/models/transformer_2d.py

@@ -200,7 +200,7 @@ class Transformer2DModel(ModelMixin, ConfigMixin):
         if self.is_input_continuous:
             # TODO: should use out_channels for continous projections
             if use_linear_projection:
-                self.proj_out = nn.Linear(in_channels, inner_dim)
+                self.proj_out = nn.Linear(inner_dim, in_channels)
             else:
                 self.proj_out = nn.Conv2d(inner_dim, in_channels, kernel_size=1, stride=1, padding=0)
         elif self.is_input_vectorized: