arm64: dts: imx8mq-librem5: lower the mipi csi 1 frequencies

No frames are streamed when using the default frequencies. I'm not yet
sure why the fastest ones don't work here but we've been using these
frequencies successfully for a long time now.
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq-librem5.dtsi

@@ -1143,6 +1143,7 @@ &lcdif {
 };
 
 &mipi_csi1 {
+	assigned-clock-rates = <266000000>, <200000000>, <66000000>;
 	status = "okay";
 
 	ports {