media: v4l: Convert the users of v4l2_get_link_freq to call it on a pad

Call v4l2_get_link_freq() on a pad, instead of a control handler. This way
we can soon convert v4l2_get_link_freq() to be callable only on a pad and
remove the compatibility code.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Naushir Patuck <naush@raspberrypi.com> # rp1-cfe
Acked-by: Benjamin Mugnier <benjamin.mugnier@foss.st.com> # st-mipid02
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>