Fix obvious typos in flax decoder impl (#17279)

Change config.encoder_ffn_dim -> config.decoder_ffn_dim for decoder.

templates/adding_a_new_model/cookiecutter-template-{{cookiecutter.modelname}}/modeling_flax_{{cookiecutter.lowercase_modelname}}.py

@@ -1996,7 +1996,7 @@ class Flax{{cookiecutter.camelcase_modelname}}DecoderLayer(nn.Module):
         )
         self.encoder_attn_layer_norm = nn.LayerNorm(dtype=self.dtype)
         self.fc1 = nn.Dense(
-            self.config.encoder_ffn_dim,
+            self.config.decoder_ffn_dim,
             dtype=self.dtype,
             kernel_init=jax.nn.initializers.normal(self.config.init_std),
         )
@@ -2997,10 +2997,10 @@ FLAX_{{cookiecutter.uppercase_modelname}}_CONDITIONAL_GENERATION_DOCSTRING = """
     ```python
     >>> import jax
     >>> from transformers import {{cookiecutter.camelcase_modelname}}Tokenizer, Flax{{cookiecutter.camelcase_modelname}}ForConditionalGeneration
-    
+
     >>> model = Flax{{cookiecutter.camelcase_modelname}}ForConditionalGeneration.from_pretrained('{{cookiecutter.checkpoint_identifier}}')
     >>> tokenizer = {{cookiecutter.camelcase_modelname}}Tokenizer.from_pretrained('{{cookiecutter.checkpoint_identifier}}')
-    
+
     >>> TXT = "My friends are <mask> but they eat too many carbs."
     >>> input_ids = tokenizer([TXT], return_tensors='np')['input_ids']