vmstate: fix varrays with uint32_t indexes

VMSTATE_VARRAY_UINT32() is used in hw/ds1225y.c, and we checked
VMS_VARRAY_UINT32 bit of field->flags in vmstate_load_state(),
but we don't check this bit in vmstate_save_state().

Signed-off-by: Amos Kong <akong@redhat.com>
Acked-by: Juan Quintela <quintela@redhat.com>
Acked-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
