[media] cx23885: use video_drvdata to get cx23885_dev pointer

Use video_drvdata(file) instead of fh->dev to get the cx23885_dev
pointer. This prepares for the vb2 conversion where fh->dev (renamed
to fh->q_dev in this patch) will be removed completely.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>