[Fix doc example] FlaxVisionEncoderDecoder (#15626)
* Fix wrong checkpoint name: vit
* Fix missing import
* Fix more missing import
* make style
* Apply suggestions from code review
Co-authored-by: NielsRogge <48327001+NielsRogge@users.noreply.github.com>
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>
Co-authored-by: NielsRogge <48327001+NielsRogge@users.noreply.github.com>