[Cin] nv-codec-headers location

[Andrew Randrianasulu]

Hello!

I was  rebuilding CinelerraGG with ffmpeg git, and noticed it started to fail due to something missed
in nv-codec-headers. I looked into downloads.txt and tried to use URL provided there,
but it was not working, in sense there was no web-interface

Web interface lives at https://git.videolan.org/?p=ffmpeg/nv-codec-headers.git

May be they should be pulled if --with-git-ffmpeg added to confugure arguments?
But for now I just passed --without-nv argument to configure