cleanup: make sure we use the right Offset

[systay]

Description

Minor clean-up: we were looking for *Offset, but the type used is Offset.
The end-result was the same, but we were taking an unnecessarily long way to get there.

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.75%. Comparing base (696fe0e) to head (9247cad).
Report is 153 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15576      +/-   ##
==========================================
- Coverage   67.41%   65.75%   -1.67%     
==========================================
  Files        1560     1561       +1     
  Lines      192752   194830    +2078     
==========================================
- Hits       129952   128107    -1845     
- Misses      62800    66723    +3923     

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[dbussink]

The end-result was the same, but we were taking an unnecessarily long way to get there.

Do we need to back port this to stay consistent?

[systay]

Do we need to back port this to stay consistent?

I don't think that is important