Get different weights from model.get_input_embeddings()
### System Info

```shell
@patil-suraj, @patrickvonplaten

- `transformers` version: 4.10.0
- Platform: macOS-10.16-x86_64-i386-64bit
- Python version: 3.8.3
- PyTorch version (GPU?): 1.11.0 (False)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: <fill in>
- Using distributed or parallel set-up in script?: <fill in>
```


### Who can help?

_No response_

### Information

- [ ] The official example scripts
- [ ] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

```py
from transformers import GPT2Config, GPT2LMHeadModel
config = GPT2Config.from_pretrained("gpt2")
model = GPT2LMHeadModel(config=config)
# print (model1.get_input_embeddings().weight.shape)
arr = model.get_input_embeddings().weight.detach().numpy()
print (arr)
print (arr.shape)
```


<img width="573" alt="image" src="https://user-images.githubusercontent.com/27731754/175279258-f0551493-2c42-4dbd-a17f-257d8298ae7c.png">

### Expected behavior

```shell
I think `model.get_input_embeddings()` should give same weights every time when it was called
```

Sorry, I made a mistake. I got answer from the documents.

> config (:class:`~transformers.GPT2Config`): Model configuration class with all the parameters of the model.
        Initializing with a config file does not load the weights associated with the model, only the
        configuration. Check out the :meth:`~transformers.PreTrainedModel.from_pretrained` method to load the model
        weights.

I need use `GPT2LMHeadModel.from_pretrained("gpt2")` rather than `GPT2LMHeadModel(config=config)`