piix4: disable io on reset

io base register at 0x40 is cleared on reset,
but io is not disabled until some other event
happens to call pm_io_space_update.

Invoke pm_io_space_update directly to make this
consistent.

Cc: qemu-stable@nongnu.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>