[media] em28xx: get rid of duplicate function vidioc_s_fmt_vbi_cap()

vidioc_s_fmt_vbi_cap() is a 100% duplicate of vidioc_g_fmt_vbi_cap() and
therefore can be removed.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>