media: uapi: vp8: Fix kernel-doc warnings

Fix following warnings:

./scripts/kernel-doc --none include/uapi/linux/v4l2-controls.h

        include/uapi/linux/v4l2-controls.h:1727: warning: bad line:
        include/uapi/linux/v4l2-controls.h:1853: warning: expecting prototype for struct v4l2_vp8_frame. Prototype was for struct v4l2_ctrl_vp8_frame instead
        include/uapi/linux/v4l2-controls.h:1853: warning: Function parameter or member 'segment' not described in 'v4l2_ctrl_vp8_frame'
        include/uapi/linux/v4l2-controls.h:1853: warning: Function parameter or member 'entropy' not described in 'v4l2_ctrl_vp8_frame'
        include/uapi/linux/v4l2-controls.h:1853: warning: Function parameter or member 'coder_state' not described in 'v4l2_ctrl_vp8_frame'

Reported-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>