migration: pre_save return int

Modify the pre_save method on VMStateDescription to return an int
rather than void so that it potentially can fail.

Changed zillions of devices to make them return 0; the only
case I've made it return non-0 is hw/intc/s390_flic_kvm.c that already
had an error_report/return case.

Note: If you add an error exit in your pre_save you must emit
an error_report to say why.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170925112917.21340-2-dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
index fa8b969..5ccd785 100644
--- a/hw/ppc/spapr_iommu.c
+++ b/hw/ppc/spapr_iommu.c
@@ -140,7 +140,7 @@
     return ret;
 }
 
-static void spapr_tce_table_pre_save(void *opaque)
+static int spapr_tce_table_pre_save(void *opaque)
 {
     sPAPRTCETable *tcet = SPAPR_TCE_TABLE(opaque);
 
@@ -149,6 +149,8 @@
 
     trace_spapr_iommu_pre_save(tcet->liobn, tcet->mig_nb_table,
                                tcet->bus_offset, tcet->page_shift);
+
+    return 0;
 }
 
 static uint64_t spapr_tce_get_min_page_size(IOMMUMemoryRegion *iommu)