Increase logging severity level for SW fallback.

This will help debugging issues with the fallback, in cases where
only LS_WARNING logs are available.

BUG=none

Review-Url: https://codereview.webrtc.org/3007523002
Cr-Original-Commit-Position: refs/heads/master@{#19488}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 955d7f19e86953c58138b432774d375358817fd1
2 files changed