[media] em28xx-v4l: fix disabling ioctl VIDIOC_S_PARM for vbi devices

Fixes an old copy+paste bug that has survived all recent code
changes in this code area.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>