XXX openbios update
PPC: Mac: Fix guest exported tbfreq values

We can tell the guest the frequency of its time base through fwcfg.

However, we tell it a different value from the speed tb actually runs
at. Let's fix it and make the tbfreq initialization and the fwcfg exposure
use the same values.

Signed-off-by: Alexander Graf <agraf@suse.de>