Update load_mat_style.m

[ehennestad]

Fix #601

Motivation

Fix issue which arise when loading 1D vectors in MATLAB R2024b due to changes to the ind2sub function as described here:
https://se.mathworks.com/help/releases/R2024b/matlab/ref/ind2sub.html?searchPort=49569#mw_463053e0-3bc5-40de-88c3-5887f667b5d3

How to test the behavior?

Loading NWB-file with a file-create date should not produce error in MATLAB R2024

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?