dt-bindings: media: imx258: Make clocks property required

dt-bindings: media: imx258: Make clocks property required

The sensor requires an external clock, and drivers need to access the
clock to retrieve its frequency in order to configure the sensor. This
makes usage of the clocks property mandatory for a system to work
properly. Mark the property as required.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>