kvm: remove redundant registration of BSP's hv_clock area

These days hv_clock allocation is memblock based (i.e. the percpu
allocator is not involved), which means that the physical address
of each of the per-cpu hv_clock areas is guaranteed to remain
unchanged through all its lifetime and we do not need to update
its location after CPU bring-up.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>