Fixing a bug in expand_rate calculation for stereo signal.
Fixing a bug in expand_rate calculation for stereo signal.

BUG=
R=henrik.lundin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/41849004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8307}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c11348b5d7163a040d777d1cfedafde758d461e0

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