Blender Git Loki

x264: update URL and hash in versions.cmake

The old URL did have a Git commit hash in it, but apparently the server
was ignoring it and only used the `master` that was also mentioned in the
URL. As a result, every new download would get the latest version from
the `master` branch, invalidating the SHA256 checksum.

I replaced `master` with the actual commit hash. This should make the
situation stable.

No functional changes.