minor fix for config class

modeling_flamingo.py

@@ -16,6 +16,7 @@ from transformers.models.opt.modeling_opt\
 from transformers import ViTModel
 from .utils import exists, freeze_all_layers_, unfreeze_all_layers_
 from .flamingo_pytorch import GatedCrossAttentionBlock, PerceiverResampler
+from .configuration_flamingo import FlamingoConfig
 
 
 class OPTLearnedPositionalEmbedding(nn.Embedding):
@@ -357,6 +358,7 @@ class FlamingoForCausalLM(modeling_opt.OPTForCausalLM):
     _keys_to_ignore_on_load_missing = [
             r"lm_head.weight",
             ]
+    config_class = FlamingoConfig
 
     def __init__(self, config):
         OPTPreTrainedModel.__init__(self, config)