media: videodev2.h: add missing __user to p_h264_pps

The p_h264_pps pointer in struct v4l2_ext_control was missing the
__user annotation. Add this.

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