pcie: don't skip multi-mask events

pcie: don't skip multi-mask events

If we are trying to set multiple bits at once, testing that just one of
them is already set gives a false positive. As a result we won't
interrupt guest if e.g. presence detection change and attention button
press are both set. This happens with multi-function device removal.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>