arm64: dts: imx8mn-beacon: Remove unnecessary clock configuration

Since commit 8208181fe5 ("clk: imx: composite-8m:
Add imx8m_divider_determine_rate") the lcdif controller has
had the ability to set the disp_pixel_clk rate which propagates
up the tree and sets the video_pll rate automatically.

As such, there is no need to define it in the board file.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mn-beacon-kit.dts

@@ -99,8 +99,6 @@ adv7535_out: endpoint {
 };
 
 &lcdif {
-	assigned-clocks = <&clk IMX8MN_VIDEO_PLL1>;
-	assigned-clock-rates = <594000000>;
 	status = "okay";
 };