V4L/DVB (12382): gspca - main: Remove vidioc_s_std().

The vidioc_s_std() is not necessary when vdev->tvnorms == 0.

Signed-off-by: Marton Nemeth <nm127@freemail.hu>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>