Remove unused macro function "v4l2_dev_to_iss_device(dev)".

Signed-off-by: Aline Santana Cordeiro <alinesantanacordeiro@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>