vp9-svc: Fix the bitrate control for spatial svc

Make sure to initialize the layer context for spatial-svc
which has a single temporal layer.

Change-Id: I026ecec483555658e09d6d8893e56ab62ee6914b
(cherry picked from commit 1e9929390c8c18ffda02e0073481625e5afb2529)
2 files changed