hantro: Move hantro_enc_buf_finish to JPEG codec_ops.done

hantro_enc_buf_finish is used only for JPEG, and so should
be moved to JPEG codec_ops.done.

This cleanup is also taking care of addressing
a subtle issue: checking the non-NULL bounce buffer
using ctx->jpeg_enc, which is a member of a union is
confusing and error-prone.

Note that the issue is currently innocuous because an
encoder context only supports JPEG.

The codec_ops.done has an argument that codec-specific code
shouldn't need, so drop that as well.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>