[media] tw5864: crop picture width to 704

Previously, width of 720 was used, but it gives 16-pixel wide black bar
at right side of encoded picture.

Signed-off-by: Andrey Utkin <andrey.utkin@corp.bluecherry.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>