[media] drivers/media/video/tlg2300/pd-video.c: Remove second mutex_unlock in pd_vidioc_s_fmt

Error path in file drivers/media/video/tlg2300/pd-video.c:
1. First mutex_unlock on &pd->lock in line 767 (in function that
   called from line 805)
2. Second in line  806

 805        pd_vidioc_s_fmt(pd, &f->fmt.pix);
 806        mutex_unlock(&pd->lock);

Found by Linux Device Drivers Verification Project

Signed-off-by: Alexander Strakh <strakh@ispras.ru>
Acked-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>