media: pvrusb2: Do not check for V4L2_CTRL_WHICH_DEF_VAL

The framework already checks for us if V4L2_CTRL_WHICH_DEF_VAL is
written.

Cc: Mike Isely <isely@pobox.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>