arm64: dts: freescale: Fix VPU G2 clock

Set VPU G2 clock to 300MHz like described in documentation.
This fixes pixels error occurring with large resolution ( >= 2560x1600)
HEVC test stream when using the postprocessor to produce NV12.

Fixes: 4ac7e4a8 ("arm64: dts: imx8mq: Enable both G1 and G2 VPU's with vpu-blk-ctrl")
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq.dtsi

@@ -772,7 +772,7 @@ pgc_vpu: power-domain@6 {
 									 <&clk IMX8MQ_SYS1_PLL_800M>,
 									 <&clk IMX8MQ_VPU_PLL>;
 						assigned-clock-rates = <600000000>,
-								       <600000000>,
+								       <300000000>,
 								       <800000000>,
 								       <0>;
 					};