hvm/hpet: In hpet_save, correctly compute mc64.

When the master clock is not enabled, mc64 has the right value.

Basicly do the same thing as hpet_read_maincounter().

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

xen/arch/x86/hvm/hpet.c

@@ -499,7 +499,8 @@ static int hpet_save(struct domain *d, hvm_domain_context_t *h)
     spin_lock(&hp->lock);
 
     /* Write the proper value into the main counter */
-    hp->hpet.mc64 = hp->mc_offset + guest_time_hpet(hp);
+    if ( hpet_enabled(hp) )
+        hp->hpet.mc64 = hp->mc_offset + guest_time_hpet(hp);
 
     /* Save the HPET registers */
     rc = _hvm_init_entry(h, HVM_SAVE_CODE(HPET), 0, HVM_SAVE_LENGTH(HPET));