[media] tvp5150: fix tvp5150_fill_fmt()

The tvp5150 output video is interlaced so mark the format
field as alternate and reduce the height to the half.

[javier: split patch and write commit message]

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>