This fixes misprint in the code which calculates target bitrate of a VP9 spatial layer where "-" was used instead of "+". Bug: none Change-Id: I17d76a84d00e453c055c068968d7b276e9c23f51 Reviewed-on: https://webrtc-review.googlesource.com/71663 Commit-Queue: Sergey Silkin <ssilkin@webrtc.org> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22974}