avcodec: vaapi: fix vout recreation on flush
Fixes #29434 (closed)
From @Courmisch
From the changeset, I guess that you want to destroy the VA-API video decoding context while retaining the VA-API display context. But then you need to destroy the instance and create a new one, not "restart". You can't just assume that the new parameters will work.
This MR now check if the new parameters match with the previous one.