Inference doesn't run on cpu only device

[JDups]

Attempting to run inference.run_inference() with device='cpu' on a Google colab CPU only instance produces an error.

RuntimeError: Found no NVIDIA driver on your system. Please check that you have an NVIDIA GPU and installed a driver from http://www.nvidia.com/Download/index.aspx

I worked around this by commenting out lines 30 to 32 of /ldm/models/diffusion/ddim.py. I am not sure if this will cause problems elsewhere that I haven't noticed.

[egeozguroglu]

Hi, we haven't tested on CPU-based inference or Google Colab, given the compute requirements. Your solution should be fine as a workaround.