V4L/DVB (6776): ivtv: Some general fixes

Fix "warning: Using plain integer as NULL pointer".
Convert 'x < y ? x : y' to use min() instead.

Signed-off-by: Richard Knutsson <ricknu-0@student.ltu.se>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>