benchmark

CMake: unbreak version handling for tarballs (#1793)

#1742 changed the placeholder version from `0.0.0` to `v0.0.0`,
but this line which was further dealing with it, was not updated.

Fixes https://github.com/google/benchmark/issues/1792

Co-authored-by: dominic <510002+dmah42@users.noreply.github.com>