media: s5p-jpeg: fix kernel-doc warnings

- added missing 'struct' kernel-doc keywords
- add missing '*' in kernel-doc comment blocks

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>