Regression since c10d498b.
Unfortunately ff_thread_get_format can only be called from
a separate decode thread, running it during init will fail.
Fixes for that are welcome, for now just revert back to
calling avctx->get_format directly, which is correct
but having to decide on a case-by-case basis which approach
to use is a bit messy.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>