[`BiT`] Small patch fix
# What does this PR do?

This PR fixes a tiny issue that you can encounter if you load `BiT` in fp16.
`diffusers` uses this model under the hood for Depth Estimation inpainting and users get this error:
```
    593 
    594         layer_dropouts = [
--> 595             x.tolist() for x in torch.linspace(0, config.drop_path_rate, sum(config.depths), dtype=torch.float32).split(config.depths)
    596         ]
    597 

RuntimeError: "linspace_cpu" not implemented for 'Half'

```
However on `diffusers` side this can be fixed by installing `accelerate` and load the pipeline with `low_cpu_mem_usage=True`. But better to fix it to avoid any misleading issue


cc @sgugger @patil-suraj 

Otherwise to reproduce:
```
import torch
from transformers import BitModel

model = BitModel.from_pretrained("google/bit-50", torch_dtype=torch.float16)
```
_The documentation is not available anymore as the PR was closed or merged._