Avoid sketchy integer cast in cbt code

Avoid sketchy integer cast in cbt code

When calling circuit_build_times_shuffle_and_store_array, we were
passing a uint32_t as an int.  arma is pretty sure that this can't
actually cause a bug, because of checks elsewhere in the code, but
it's best not to pass a uint32_t as an int anyway.

Found by doorss; fix on 0.2.2.4-alpha.