Documentation: media: camera-sensor: Mention v4l2_devm_sensor_clk_get() for obtaining...

Documentation: media: camera-sensor: Mention v4l2_devm_sensor_clk_get() for obtaining the clock

Add the new v4l2 helper devm_v4l2_sensor_clk_get() to Documentation. the
helper works on both DT- and ACPI-based platforms to retrieve a
reference to the clock producer from firmware.

Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Co-developed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>