Merge commit 'c8e135ea9225137050a6315fd9ba9c0f242c90b6'

Merge commit 'c8e135ea9225137050a6315fd9ba9c0f242c90b6'

* commit 'c8e135ea9225137050a6315fd9ba9c0f242c90b6':
  vaapi_encode: Allocate slice structures and parameter buffers dynamically

Already present as e4a6eb70f471eda36592078e8fa1bad87fc9df73, one minor
fix for libav merged.

Merged-by: Mark Thompson <sw@jkqxz.net>