This fixes a use-after-free if do_address_space_destroy is executed
too late.
Reviewed-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Tested-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>