vrend: fix -Wformat for hex format print of uint64_t
To unblock the failed uprev: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/5717012
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To unblock the failed uprev: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/5717012