There are instructions that take 7 bytes, e.g.
4881ec10000000 REX.W subq rsp,0x10

Hence increase the padding from 12 characters to 14 characters to
restore alignment.

Drive-by: Rewrite the padding loop to make it more readable and add a
comment.

R=jkummerow@chromium.org

Change-Id: Iddd6a721574fc47b4a072fe40c2f5e90cb3d1186
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2996200Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75480}