arm64: dts: imx8mq-librem5: Limit uSDHC2 frequency to 50MHz

SparkLAN card has stability issues at 100MHz. It still appears to be
able to max out its throughput this way, so limit the frequency to
ensure stable operation.

Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Author: dos1

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

@@ -1424,7 +1424,7 @@
 
 &usdhc2 {
 	assigned-clocks = <&clk IMX8MQ_CLK_USDHC2>;
-	assigned-clock-rates = <200000000>;
+	assigned-clock-rates = <50000000>;
 	pinctrl-names = "default", "state_100mhz", "state_200mhz";
 	pinctrl-0 = <&pinctrl_usdhc2>;
 	pinctrl-1 = <&pinctrl_usdhc2_100mhz>;
@@ -1434,7 +1434,7 @@
 	mmc-pwrseq = <&usdhc2_pwrseq>;
 	post-power-on-delay-ms = <20>;
 	cd-gpios = <&gpio2 12 GPIO_ACTIVE_LOW>;
-	max-frequency = <100000000>;
+	max-frequency = <50000000>;
 	disable-wp;
 	cap-sdio-irq;
 	keep-power-in-suspend;