arm64: dts: rockchip: rename HDMI ref clock to 'ref' on rk3399

The reference clock for the HDMI controller has been renamed to 'ref',
the previous 'vpll' name is only left for compatibility in the driver.
Rename the clock to the new name.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Michael Riesch <michael.riesch@wolfvision.net>
Link: https://lore.kernel.org/r/20220422072841.2206452-7-s.hauer@pengutronix.de


Signed-off-by: Heiko Stuebner <heiko@sntech.de>