From reading the code it was totally unclear what the purpose of the
"offset" parameter at ProcessCodeSectionHeader and CheckFunctionsCount
is. Actually, it's just there for setting an error position. Thus this
CL renames the field, and a related local variable to make the use more
clear.

Drive-by: Remove a confusing and unnecessary Decoder::Reset call.

R=ahaas@chromium.org

Change-Id: Iccde5ccb3b9e7e52976c47724157c184fd345ec4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567709Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71563}