[media] media/usb/pvrusb2: Support for V4L2_CTRL_WHICH_DEF_VAL

This driver does not use the control infrastructure.
Add support for the new field which on structure
 v4l2_ext_controls

Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>