ARM: dts: lager: Move cec_clock to root node

cec-clock is a fixed clock generator that is not controlled by i2c-12
and thus should not be a child of the i2c-12 bus node. Rather, it should
be a child of the root node of the DT.

Fixes: c5aa8797 ("ARM: dts: lager: Add CEC clock for HDMI transmitter")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>