media: mtk-jpeg/mtk_jpeg_core.h: fix kernel-doc warnings

Add missing 'struct' keywords and fix typos in two struct member
names.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Xia Jiang <xia.jiang@mediatek.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>