Properly support capture start on em2874

The transport stream enable register moved in the em2874, so make it work
properly.

Thanks for Ray Lu from Empia for providing the em2874 datasheet.
Signed-off-by: Devin Heitmueller <devin.heitmueller@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>