V4L/DVB (6714): ivtv: yuv frame parameter fix

Inadvertently missed a line when converting code to new hardware buffering
method. In some circumstances, this would lead to a frame being displayed
using parameters belonging to another frame.

Signed-off-by: Ian Armstrong <ian@iarmst.demon.co.uk>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>