NetEq: Minor follow-up fix in StatisticsCalculator

This change follows the recommendation of a post-commit comment in
r9778:
https://codereview.webrtc.org/1296633002/diff/100001/webrtc/modules/audio_coding/neteq/statistics_calculator.cc#newcode198

TBR=pkasting@chromium.org

Review URL: https://codereview.webrtc.org/1319953002

Cr-Original-Commit-Position: refs/heads/master@{#9803}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1e346b20c430bbfab650db6524e39721851bcf2e
1 file changed