V4L/DVB (12453a): DaVinci: DM646x: Update the structure name as per header file changes

In the platform header file, the subdev_info structure name has been changed
to vpif_subdev_info. Update this change in the driver too.

Applies to v4l-dvb repository.

Signed-off-by: Chaithrika U S <chaithrika@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>