media: s5p-mfc/s5p_mfc_common.h: fix kernel-doc warnings

Trivial fixes for many kernel-doc warnings. Most of the comments before
enums or struct can just be that: regular comments.

So just change /** to /*.

In one remaining case it was just a wrong construct: @mem_dev[] -> @mem_dev

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>