media: dt-bindings: nokia,smia: Fix link-frequencies documentation

The link-frequencies property belongs to the endpoint, not to the node
representing the device.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>