V4L/DVB (10814): saa7146: some small fixes

vidioc_enum_fmt_vid_overlay() did nothing but call
vidioc_enum_fmt_vid_cap(), so just make
saa7146_video_ioctl_ops.vidioc_enum_fmt_vid_overlay point to
vidioc_enum_fmt_vid_cap() and get ride of vidioc_enum_fmt_vid_overlay().

Have gparm use v4l2_video_std_frame_period to fill in the frame period
instead of just assuming PAL.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>