hvm/hpet: In hpet_save, call hpet_get_comparator.

hvm/hpet: In hpet_save, call hpet_get_comparator.

This changes save data to consistent/expected values.  It is not
technically required because hpet_get_comparator() will adjust from
any value to the correct value. And hpet_get_comparator() is
effectivly called in hpet_load via hpet_set_timer.

However it does look strange to people that the output from
xen-hvmctx for the comparator values do not change when the master
clock does.

The software-developers-hpet-spec-1-0a.pdf says that the comparator
will allways be greater than master clock for a periodic timer.

Signed-off-by: Don Slutz <dslutz@verizon.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>