[media] tw686x-video: test for 60Hz instead of 50Hz

When determining if the standard is 50 or 60 Hz it is standard
practice to test for 60 Hz instead of 50 Hz.

This doesn't matter normally, except if the user specifies both
60 and 50 Hz standards.

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