vhost: fix dirty page handling

vhost was passing a physical address to cpu_physical_memory_set_dirty,
which is wrong: we need to translate to ram address first.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Note: this lead to crashes during migration, so the patch
is needed on the stable branch too.

hw/vhost.c

@@ -47,8 +47,10 @@ static void vhost_dev_sync_region(struct vhost_dev *dev,
         log = __sync_fetch_and_and(from, 0);
         while ((bit = sizeof(log) > sizeof(int) ?
                 ffsll(log) : ffs(log))) {
+            ram_addr_t ram_addr;
             bit -= 1;
-            cpu_physical_memory_set_dirty(addr + bit * VHOST_LOG_PAGE);
+            ram_addr = cpu_get_physical_page_desc(addr + bit * VHOST_LOG_PAGE);
+            cpu_physical_memory_set_dirty(ram_addr);
             log &= ~(0x1ull << bit);
         }
         addr += VHOST_LOG_CHUNK;