This is a minor cosmetic fix. Wasm opcodes are bytes, hence they should
always be printed as an even number of hexadecimal digits.
Note that currently we only print a single byte anyway, but in the
future we will want to extend this to correctly parse multi-byte
opcodes. Those will also be printed as an even number of characters
then.

R=thibaudm@chromium.org

Bug: v8:10351
Change-Id: I2423277b470d74c1c72cb619c2a43bb978423bc0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2122025Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66883}