media: zoran: Use video_drvdata to get struct zoran

Using video_drvdata() is proper and shorter than using directly
fh pointers.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>