block/iscsi: fix memory corruption on iscsi resize bs->total_sectors is not yet updated at this point. resulting in memory corruption if the volume has grown and data is written to the newly availble areas. CC: qemu-stable@nongnu.org Signed-off-by: Peter Lieven <pl@kamp.de> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>