V4L/DVB (4637): Add a default method for VIDIOC_G_PARM

For most drivers, VIDIOC_G_PARM will just return the current standard fps.
So, instead of failing, drivers based on video_ioctl2 will implement the
default method.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>