media: sh_veu: convert to struct v4l2_fh

This driver didn't use struct v4l2_fh, so add it.

This is a very basic conversion. I can't test this on real hardware,
so I didn't dare to also convert the driver to start using the
v4l2-mem2mem ioctl/fop helpers.

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